For instance, if you just use "regular" HTML, will people still be able to see and use my website normally, even if they are not using Internet Explorer? For example, I always use Firefox. Other people use things like AOL or Opera to browse the web. Thanks for your help!
There’s no such thing as a silly question. Don’t worry; HTML will work across all browsers. However, bear in mind that html does have different ‘dialects’ depending on whether you’re using strict, transitional, or frameset (this goes in the doc type declaration or DTD at the top of a html page) plus older browsers such as IE6 can be quirky and not show websites exactly as they should. Just use strict and xhtml (which is a cleaner, stricter version of HTML) and you should be okay in most modern browsers. Visit http://www.freewebtutorial.co.uk (web standards section) for more info.
Hope this helps.