Check it out and let me know what you think. One of the coolest things is a new tool webTune2600... actually just a friendly wrapper to Thomas Jentzsch's old Tune2600. Just check the notes you want off the piano or guitar UI and hit the button, and it will return the values to use.
Music on the Atari 2600 is a little odd. To put it simply, the way an Atari makes sounds means it can't play the "normal" notes that make up Western music.
The good news is that batari BASIC makes it pretty easy to experiment with the sound capabilities of the 2600. It doesn't have built in sound commands, per se, but it's pretty easy to write the logic to set the 6 special TIA variables that control what's coming out of your TV speakers while your bB program is under way.
(Incidentally, everything in this page (except for the code samples) applies to people coding in ASM as well.)
The 2600 can play two tones at once. It has several different "voices" ("distortions") that either voice can be set to (some good for music, some good for sound or drum effects), and each voice is set to one of 32 values that control the pitch.
This page can't make a musician out of you...it will help if you know the very basics of music: what notes are, and how letters are used to describe notes and all that stuff. Also, this page will mostly discuss music, not ideas for Sound Effects, which have to share the same two voices.