Css coding = confusing

Hello everyone!
My friend suggested I sign up to this site, and I have to admit, I love how peaceful it is here. It's so unique!

I would like to blog, but when it comes to using css codes, I'm at a loss.
Everyone has such appealing blogs, and I'm afraid mine will pale in comparison

My friend taught me how to bold words
Italicize
Underline

And also how to enlarge text and colour but nothing else
and I don't know where to go for help, as that is all she knows

Any suggestions?

And as a side question, are all css codes the same, or are there different ones for different sites? (like Endless Forest)
This may be a silly question, but I don't understand css coding at all.