One thing to be aware of is that you will need a Paypal account to sell. That is how you get paid. Basically, TpT takes care of all the sales transactions and then pays you once a quarter through PayPal (unless you make over $500 in a quarter, then you get a paper check, a nice goal to shoot for). Paypal is free, easy and secure, so go ahead and get one.
Next you get to fill in some basic information - don't worry about your user name, that is NOT your the name that will appear on your TpT profile or store, You get to choose that later. (you will also have an opportunity to opt out of using your real name on the site, so if you want to be the Batman of TpT and use an alias, you can totally do that, and in fact, many sellers do.) Once you finish registering, you will get an email with some nifty suggestions about what to do next. They are in fact, quite nifty, and you should follow them.
So, are you ready to sign up? You can do it right here or click on the pictures at the top of this post.
Then come right back here and get some good tips for how to Set Up Your Profile.