If you want to test how fast your website loads from different places around the world this is a killer tool for that. You should be shooting for under 3 seconds.
It also shows you a graph of when things load and how long they take so you can diagnose issues.
If you want to make Google happy and view their idea of PageSpeed insights on desktop and mobile then use this link here.
It will give you a score from 0-100 for both desktop and mobile and tells you exactly what you need to do to fix it. Pretty cool tool from Google.