Many people don't realize that when they visit web sites, they aren't necessarily seeing the most up-to-date version of each page. Web browsers incorporate something called a "cache", which is a collection of recently-visited pages. Depending on how your browser's options are set, and to some extent how the page is coded, the browser will try to save time when you try to visit an address (URL); if the browser finds a copy of the page in its cache, it may just display that.
There are various ways to force the browser to fetch a fresh copy from the server; clearing out the cache is the quickest way to take care of it, especially if there are multiple pages involved.
When you're viewing other peoples' sites, the fact that you may be seeing old versions of their pages may be just a minor inconvenience -- you may miss seeing the current temperature, for example, or the correct score of some sporting event.
But once you start putting your own content out on the web, and making changes, it can be really alarming to look at your site and see some old stuff!
So just remember that cache idea. Depending on the browser, Ctrl-F5, or Shift-Reload, or something similar may be the key to forcing a fresh fetch of the page you're looking at.
