For your benefit, below are training videos that will demonstrate each of the altar server duties and at what part of the Mass you will be expected to perform the duties. You are expected to know how to perform all duties if called upon.
Exceptions include 5th and 6th grade servers and new altar servers that have not yet received and demonstrated proficiency in all duties. They will have limited duties throughout the first year of altar serving. Additional training is required for the duties of crucifer (cross bearer) and candle bearers.
Novices should serve 10 masses to be eligible for candle bearers and crucifer training. To bear the cross also carries a height requirement - you must be able to hold the heavy cross and place it on the post. You must be at least 5' tall to manage that.
An additional 15 masses of experience with prayer hands/crucifer/candle bearer is required before one can train for thurifer.
Bishop training is done on demand prior to the mass one will serve with the Bishop. Only those who are full altar servers (through to crucifer/candle holder) can serve the Bishop.