Learn through practice, application, and persistence.
FireFox is far more standards compliant than any version of Internet Explorer; it uses the Gecko rendering engine which is not only open-source but, again, standards compliant. Trust me, IE is the culprit in breaking 'perfectly good sites' (I hate that browser with a passion).
You should build your site to accommodate FireFox, then tweak it for Internet Explorer.
You need to learn XHTML (screw HTML, that is old), proper doctype declarations, CSS (Cascading Style Sheets) and then you could move on. You should be able to write an entire site by hand without any WYSIWYG editors; it will be empowering for you and also aide in higher quality documents that you produce.
W3Schools is a great learning resource - I frequently use it for reference.