E.g. The site is slow.
To test this site’s speed, to see if it’s on our end or your ISP or PC, you can visit this page. Assuming the site loads in 7 seconds or less on that page, it means the site itself is delivering appropriate speeds, allowing you to look at your ISP or local PC for a possible cause.
To test your internet latency and speed (both scores can affect your experience on some parts of the web, depending on the routes taken by your ISP), visit speedtest.net. High latency is common on satellite connections or 3G/4G routers (e.g. Mifi). Broadband speeds are roughly something above 1.75mbps. Running 3 tests and getting an average for latency and speed can give you a clear picture of how your connection is doing.
If everything is testing well, but the site is still inaccessible or slow, it’s likely an issue with servers through which internet traffic is routed and the issue will likely pass – try again in 10min or so.