1: Go into iTunes.
2: Right click on the song and choose 'Get Info' (or press cmd+i on a Mac).
3: In 'Info' change the album name to the one you want it to go into, when you start typeing it should automatically come up.
4: Check that the disk number and track number is correct. It should be automatic.
4: Press OK.
You should see it go into the album now.
Kind of on the same topic, if I were to purchase the whole album after having bought the singles, would it charge me for the same songs on the album again?
My example: If I want to buy the single for the Skillet song "Sick of It" off of their album Rise, when I purchase the full album, will it take off the price for the song "Sick of It" or will it charge for the whole album album regardless of which singles I bought? Essentially, are singles recognized when it completes my album?