PageSpeed Insights is very good thing which tell u that how much time your site take to load on internet. It gives a breif variaty and google play a good role on it. Let's see how it works.
It has two parts
  1. 1 Mobile Analysis
  2. 2 Desktop Analysis

Mobile anlysis shows that how your site should be loaded in to the Andriod smart phone and how much time it takes
Desktop for PageSpeed Insights shows that how your website load on desktop system and how much time it takes.

What you have to do is simply enter the url of your website and then click on analysis button
After that what it shows the score out of 100
If you do analysis for this website www.vuhelp.net/forum.php
then what you are going to get is the 63/100 for mobile and 62/100 for desktop
Let's see what analysis we got for this website.
First for Mobile loading for vuhelp.net
63 / 100Speed

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Should Fix:
Eliminate render-blocking JavaScript and CSS in above-the-fold content
Your page has 4 blocking script resources and 2 blocking CSS resources. This causes a delay in rendering your page.
None of the above-the-fold content on your page could be rendered without waiting for the following resources to load. Try to defer or asynchronously load blocking resources, or inline the critical portions of those resources directly in the HTML.
Remove render-blocking JavaScript:
http://ajax.googleapis.com/ajax/libs.../jquery.min.js
http://www.vuhelp.net/…entscript/vbu...-init.js?v=422
http://www.vuhelp.net/…ipt/jquery/jq....0.vb.js?v=422
http://www.vuhelp.net/clientscript/v...obile.js?v=422
Optimize CSS Delivery of the following:
http://www.vuhelp.net/…t/jquery/jque....min.css?v=422
http://www.vuhelp.net/…style00002l/m...s?d=1421504539
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Enable compression
Show how to fix
Consider Fixing:
Prioritize visible content
Your page requires additional network round trips to render the above-the-fold content. For best performance, reduce the amount of HTML needed to render above-the-fold content.
The entire HTML response was not sufficient to render the above-the-fold content. This usually indicates that additional resources, loaded after HTML parsing, were required to render above-the-fold content. Prioritize visible content that is needed for rendering above-the-fold by including it directly in the HTML response.
Only about 9% of the final above-the-fold content could be rendered with the full HTML response see screenshot.
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Leverage browser caching
Show how to fix
Reduce server response time
Show how to fix
Minify JavaScript
Show how to fix
4 Passed Rules
Show details


Now for the Desktop loading for the vuhelp.net
62 / 100Suggestions Summary

Should Fix:
Eliminate render-blocking JavaScript and CSS in above-the-fold content
Your page has 11 blocking script resources and 3 blocking CSS resources. This causes a delay in rendering your page.
None of the above-the-fold content on your page could be rendered without waiting for the following resources to load. Try to defer or asynchronously load blocking resources, or inline the critical portions of those resources directly in the HTML.
Remove render-blocking JavaScript:
http://www.vuhelp.net/…r-dom-event/y...event.js?v=422
http://www.vuhelp.net/…t/yui/connect...n-min.js?v=422
http://www.vuhelp.net/clientscript/v...-core.js?v=422
http://www.vuhelp.net/clientscript/v...n_md5.js?v=422
http://rt.trafficfacts.com/…b0e8eebf...8a0h26;c=s;v=5
http://script.opentracker.net/?site=www.vuhelp.net
http://s10.histats.com/js15.js
http://s4.histats.com/…tp%3A%2F%2Fww...2Fforum.php&@w
http://www.statcounter.com/counter/counter.js
http://resources.infolinks.com/js/infolinks_main.js
http://resources.infolinks.com/js/3008.36a/ice.js
Optimize CSS Delivery of the following:
http://www.vuhelp.net/…bulletin_css/...ain-rollup.css
http://www.vuhelp.net/…tin_css/style...ome-rollup.css
http://www.vuhelp.net/…/style00001l/...s?d=1421679785
Hide details
Leverage browser caching
Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network.
Leverage browser caching for the following cacheable resources:
http://s10.histats.com/js15.js (expiration not specified)
http://www.vuhelp.net/…tin_css/style...ome-rollup.css (expiration not specified)
http://www.vuhelp.net/…bulletin_css/...ain-rollup.css (expiration not specified)
http://www.vuhelp.net/images/buttons/collapse.png (expiration not specified)
http://www.vuhelp.net/images/buttons/collapse_40b.png (expiration not specified)
http://www.vuhelp.net/images/buttons/lastpost-right.png (expiration not specified)
http://www.vuhelp.net/images/buttons/newbtn_middle.png (expiration not specified)
http://www.vuhelp.net/images/buttons/search.png (expiration not specified)
http://www.vuhelp.net/images/gradien...-grey-down.png (expiration not specified)
http://www.vuhelp.net/images/gradients/grey-up.png (expiration not specified)
http://www.vuhelp.net/…selected-tab-...-top-alpha.png (expiration not specified)
http://www.vuhelp.net/images/icons/I2.gif (expiration not specified)
http://www.vuhelp.net/images/icons/icon14.png (expiration not specified)
http://www.vuhelp.net/images/icons/plain.png (expiration not specified)
http://www.vuhelp.net/images/misc/bl...ward_arrow.png (expiration not specified)
http://www.vuhelp.net/images/misc/forum_stats.png (expiration not specified)
http://www.vuhelp.net/images/misc/legend.png (expiration not specified)
http://www.vuhelp.net/images/misc/navbit-home.png (expiration not specified)
http://www.vuhelp.net/images/misc/vbulletin4_logo.png (expiration not specified)
http://www.vuhelp.net/images/statusicon/category-16.png (expiration not specified)
http://www.vuhelp.net/images/statusi...um_link-16.png (expiration not specified)
http://www.vuhelp.net/images/statusi...rum_new-16.png (expiration not specified)
http://www.vuhelp.net/images/statusi...rum_old-16.png (expiration not specified)
http://www.vuhelp.net/images/statusi...rum_old-48.png (expiration not specified)
http://www.vuhelp.net/images/statusicon/post_old.gif (expiration not specified)
http://www.vuhelp.net/images/statusi...rum_old-48.png (expiration not specified)
http://connect.facebook.net/en_US/all.js (20 minutes)
https://apis.google.com/js/api.js (30 minutes)
https://apis.google.com/js/plusone.js (30 minutes)
http://pagead2.googlesyndication.com...adsbygoogle.js (60 minutes)
http://pagead2.googlesyndication.com/pagead/osd.js (60 minutes)
http://resources.infolinks.com/js/infolinks_main.js (60 minutes)
https://oauth.googleusercontent.com/...ig.sha1.js?c=2 (60 minutes)
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Enable compression
Compressing resources with gzip or deflate can reduce the number of bytes sent over the network.
Enable compression for the following resources to reduce their transfer size by 152.7KiB (73% reduction).
Compressing http://www.vuhelp.net/…bulletin_css/...ain-rollup.css could save 54.9KiB (82% reduction).
Compressing http://www.vuhelp.net/…r-dom-event/y...event.js?v=422 could save 40.5KiB (67% reduction).
Compressing http://www.vuhelp.net/clientscript/v...-core.js?v=422 could save 35.9KiB (70% reduction).
Compressing http://www.vuhelp.net/…tin_css/style...ome-rollup.css could save 9.4KiB (80% reduction).
Compressing http://www.vuhelp.net/…t/yui/connect...n-min.js?v=422 could save 8.6KiB (66% reduction).
Compressing http://www.vuhelp.net/clientscript/v...n_md5.js?v=422 could save 3.4KiB (63% reduction).
Hide details
Consider Fixing:
Optimize images
Show how to fix
Prioritize visible content
Show how to fix
Reduce server response time
Show how to fix
Minify JavaScript
Show how to fix
Minify HTML
Show how to fix
2 Passed Rules
Show details

It shows the rules and gives colours if u got the red colour that's mean you need to make few changes and fix the errors if you get the green colour that's mean your site is fine