Can anyone help me with tumblr?

i'm new to tumblr and i get everything except for how to customize my page, i figured out the theme and got one from dolliecrave.com but that was all i was able to do and i was able to create a title.. can anyone help me make it better looking and how do you make a custom quote thing like it show on the page when your editing it? also whats widgets/ html things are they talking about in the info tab... i'm was really great when it came to myspace(the old one), facebook, and twitter but tumblr is something totally different.