Import Newly Created Tracks into iTunes
If you have iTunes 9.x, this is very easy. You can have iTunes watch a folder to automatically include content in your iTunes library as you add songs. If you want to use this feature, you'll need to let iTunes "organize your music." This means that iTunes will create folders for albums and copy the music into them. Access this under
File → Library → Organize Library.
It takes a while, but when it's done, you'll have a new folder under
User → Music → iTunes → iTunes Music → Automatically Add to iTunes
unless it's a brand new install of iTunes, in which case it's placed in
User → Music → iTunes → iTunes Media → Automatically Add to iTunes
Put your new tracks there, and within a few minutes after starting, iTunes will notice them and import them.
But what if you don't want to have to use a particular folder and want to control your own folder hierarchy? That's fine, too. Click File → Add Folder to Library… and navigate to the top-level folder of your MP3 music collection. In other words, if you just put your MP3 in a folder called My New Album under My MP3 Music under Music, point iTunes to "Music" and it will find the downstream folders as well.
The disadvantage to this method is that you need to repeat including the folder every time you add music to it, but that's how we did it in previous versions of iTunes, anyway.