What did the bull come to atone for?
Rashi #1: It came to atone for all mundane activities and abominations that were (or would be) 1 performed on it.
Rashi #2 (citing the Toras Kohanim): It atoned for any stolen items that may have been donated regarding the work of the Mishkan and the Mizbe'ach.
Ramban (citing the Ibn Ezra): It came to atone for Aharon and his sons together with the two rams. 2
What does "v'Chiteisa es ha'Mizbe'ach" mean?
Rashi: It means that Moshe was to place the blood of the bull on the Mizbe'ach with his finger.
Rashi writes that all Meshichos were in the form of a Greek 'Kaf'. Above (verse 7), he said 'also this was like a [Greek] Chai' (like an X, and so it says in Menachos 75a)!