Tracking is the process of capturing the performance of a song. Typically instruments and voices are captured individually on separate tracks to be mixed down together to a stereo mix. Song length and complexity dictate any additional cost.
Tracks recorded with us or elsewhere are balanced against each other and then mixed down to a 2-channel stereo mix that is ready to be mastered.
This is where finished mixes are tonally balanced, stereo width is enhanced, and overall volume is brought up to commercial levels. Mastering can be as subtle as taking a mix and just making it loud and clear or imparting all sorts of vibe and character.