various

I am using Chess Mentor.  The program keeps using words I don't understand and makes references to "Variations" that I cannot seem to find on chess.com.  Can anyone define "zugzwang" and "tempo"?  Can anyone tell me how to access these "Variations"?  Thank you.

A player whose turn it is to move who has no move that does not worsen his position is said to be in zugzwang.

Tempo refers to a "turn" or single move.

Doesn't "Tempo" mean that when you are making a move, at the same time you are developing your position in a positive way, rather than just moving a piece?  

Tempo

An extra move, an initiative at development. A player gains a tempo (usually in the opening) by making the opponent move the same piece twice or defend an enemy piece. In the endgame, one may wish to lose a tempo by triangulation to gain against the opposition. (Plural: tempos or tempi).

Variation

Main article: Variation (game tree)

A sequence of moves or alternative line of play, often applied to the opening. A variation does not have to have been played in a game, it may also be a possibility that occurs only in analysis. The word Variation is also used to name specific sequences of moves within an opening. For an example, the Dragon Variation is part of theSicilian Defence.

http://en.wikipedia.org/wiki/Glossary_of_chess

Also, at the top of the page click on "Read" and then click "Chessopedia".