I'm a newbie as well. I run trac using the standalone server, tracd, and have never done anything else, so my knowledge comes from that experience. You have to change the way trac is spawned. http://trac.edgewall.org/wiki/TracStandalone documents my experience well. The syntax synopsis is at #Reference:
Tracd [options] [projenv1 [projenv2 ...]]
(I added some flair to it.) There's also a -e option that will serve every project in a directory. If you're using -e, then simply deleting the project directory (and a restart) is sufficient. If you're explicitly enumerating the project environments, you'll need to remove the project environment from the command line of trac.
If you're running behind a web server, sorry for wasting your time. :)
Welcome, and enjoy trac!
Which backend are you using? As a self confessed "noob" then I assume you probably went with the default SQLite database. As this is stored in a subdirectory of the environment (e.g. /var/lib/trac/what_I_want_to_delete/db) then, yes, you remove the "project" by deleting the folder... If you used a different database backend, then removing the folder will not remove the data from the database, you will need to use your admin tools for that (e.g. pg-admin for PostgreSQL).
I also assume that you are using the "parent path" option of listing all folders under one root as projects. If not, you will (as Aaron) says, also need to update the command / configuration used to host your tracs.
Regards,
~ mark c