what you can and can't do in all browsers.
That topic is a minefield. I generally apply the principle of standard compliant, clean code, and to Hell with a browser that can't render a simple markup correctly. Concentrate on HTML and CSS. Javascript can do some cool stuff, but make sure there is a fallback for any browser/users with javascript disabled.
The likes of IE6 can **** off. Either upgrade your browser or get off the internet.
If you want it to look good you'll need to know HTML, CSS
Truer words were never spoken. Wordpress is good, but its also largely defunct. Either you know how markup works, or you change the banner image in a template and all your page content layouts look ****.
Its like learning to play piano without learning to read music. Unless you are a savant you can probably muddle along but will mostly just suck at it.
Markup languages like HTML are incredibly simple. I can understand you not wanting to delve in to hardcore C programming, but learning to put <p>tags around words</p> is hardly taxing. Stop being lazy and LEARN IT.