If your drums are set up for Pro Mode, go to: "*****"
For Rock Band to recognize your Drum set as compatible with "Pro Drums" you are going to need at least 2 cymbals (there is no reason you should have 1). You can have up to 3 cymbals (yellow, blue, green) and a second hi-hat pedal.
Once this is plugged in and ready to go, when trying to set-up a song or training on pro, it will ask you to identify which parts of the pro set-up you have, so you select them, most likely being yellow and green cymbal. (This process is automatically comes up in-game or can be accessed through the menu)
You are ready to start. From the main men go to "Trainer", and then select "Learn an Instrument" and pick "Pro Drums". You will have a menu show up with 12 lessons, ranging in difficulty. Your goal is to complete the FIRST 3 "Introductory lessons", all beats at full speed. Once you get 100% in a beat, and don't overhit, the bar to the left will begin turning green. Move on to the next beat by using the arrow keys (go to the right) and complete all of them for all 3 lessons. (Around 15-20 beats total.) This isn't too difficult, but you do need some previous drum skill to pass this. Otherwise, you need some more training or a friend to help you press the pedal or a pad.
*Hope this helps with the process of getting the achievement, otherwise it's purely up to skill.