“Caching” is a term for saving resources from a website locally on your phone, tablet or computer. Most web-browsers do this automatically so that repeat visits to websites can load even faster.
Functionally, this means that your visitors will get to your content faster than without it, but it also means that they will use less Data if they are on a metered internet connection. However, if you are making changes to your website, this can mean that the changes will not show up for all users immediately.
If you need to clear your cache, most Windows browsers will allow you to do it on a page by page basis by pressing [CTRL] + [F5], Apple Safari, and most other browsers for Mac will do the same with [Option] + [⌘] + [E]