Question about Offsides

This I'm sure will sound like a stupid question, but Im not very knowledgeable about the sport's rules, so I figured I would ask.

It's regarding offsides.. Time and time again I see one of my players knocking in a rebound off the goalkeeper, only to have offsides called.. Is this a flaw with the game, or is that really considered offsides in real life? It just does not make much sense tome how a player can be offiside if when the opposing goalkeeper is the last person to touch the ball...

Yes he is offside, its a real life rule.

He has to be onside when the original shot is taken.

In a nutshell, there need to be two defenders between the attacking player and the goal at the time the ball is played by a member of the attacking team - this also includes shots. One of those players is normally the GK, but doesn't have to be. Note that "between the attacking player and the goal" means "further up the pitch", not in a direct line (but I take it that bit's clear). This means the offside offence actually occurs when the shot is taken, not when the keeper saves it.

There are a few caveats; you can't be offside in your own half, from a throw in, or if you're behind the ball when it's played - i.e. a cut back to a player will never result in offside even if there's no one between him and the goal.

The idea is to prevent "goal hanging" where a forward stands in the penalty area waiting for the long ball to be kicked upfield before facing the keeper 1-on-1.

I always find that the offside rule is very difficult to explain, which is why there is always the joke about women not being able to understand it.

When Player A takes the shot, Player B is in an offside position. As Player B is not interfering with play, no offside is given at the time of the shot, and had the goalkeeper not saved it then the goal would stand. However, as the goalkeeper deflects the ball to Player B, Player B is now gaining an advantage from being in an offside position at the time of the initial shot.

Yep, this is the "gaining an advantage" bit of the offside law.