Noob question conerning jQuery start-tag

Noob question conerning jQuery start-tag

I am good at PHP and I am trying to learn jQuery. My question is these start tag showing WHERE jQuery finds (and eventually) does something, like:

$('.myTR td').html(originalContent); or
$("td[contenteditable=true]").blur(function()

What I understand is that that it is looking for "myTR" and in the other case "td[contenteditable=true]". Abstractly it is a kind of regular expressions in the way that it searches for something and does something (blur/changes, whatever).

I don't understand the convention and where do I find something about these conventions? I do realize that "td[contenteditable=true]" makes the full jQuery example work (my table-ceel blurred). I just don't understand how it did it because I don't understand the convention of "searching" for things.

Hope my question makes sense :)