@tfockler60: First you sign up with Typekit. As Jennifer said, if you sign up for the free/trial version, your choice of fonts will be limited (still, quite a few to chose from). Once you sign up, you'll be given a Typekit ID which you must add to your blog. Then you go to Typekit again, click the Add button you'll see next to any of the available fonts, paste the appropriate selectors into the Selectors box, click Add, click Publish. Changes will take a few minutes to propagate.
For the content of your posts in general, the selector is:
For post titles:
Note that many selectors are theme specific: if you switch to another theme, you may have to edit the fonts you have chosen and change some of the selectors. You can see all the selectors if you go to Appearance > Edit CSS and click "view original stylesheet" (but if you have no experience in HTML and CSS, it'll be scary!). If you use Firefox, you can use an add-on (Firebug or Aardvark) that helps examine the CSS of your blog page.