After your Domain and Account are set up, you'll get an email to login to your blog's admin panel. It looks like this. The first thing you want to do is get rid of that Hello World! Post before Google finds it and keeps you indexed with "Hello World!" for a month. (Put your mous over the blue colored link with "Hello world!" and you'll see options, delete, edit.... Get rid of it and then click add new (left panel there) and Write an introductory post.
Next step. Click on Settings (see it above at the bottom of the left panel?) Then you can fill in the first two blanks. DO THIS NOW. because, if you don't, Google will find it and index you with "My Blog" and "just another WordPress weblog" which will also make you look stupid for up to a month.