I am not sure how altitude effects velocity. Some of the people that hunt the mountains would know about that. But with a rifle like you have, you really do not need to worry too much about that. The little difference altitudeis going to make should not be a life or death thing. Too much is placed on fps of a projectile. Accuracy and hitting the right spot is more important.

Read your instructions close. Goex is hard to find in many places, but keep looking. And I commend you for wanting someone to show you the ropes. The only reason I shoot all year is because of my personal range. And right now I can only shoot at 50 yards. Once the snow melts it will be different.