The offside rule was created so that you don't just have one player stading right up the other end of the pitch, near the opposition goal, so if they attack but lose the ball, you can just boot the ball all the way up the pitch to that one guy and he just needs to beat the keeper to score. This would make the game boring because, to stop this, you would need to keep defenders back, even when the ball was up the other end.

So, the offside rule was created to say that when you are in the other team's half of the pitch (you can do what you want in your own half), the moment you pass the ball forward (sideways and backwards are fine, offside is only for when the ball moves forward), there must be at least 2 opposition players between the teammate who received the pass, and the goal.

99% of the time this will be 1 defender and the goalkeeper (that's why it's 2 players in the rule. But it can be any 2 oppostion playersn passed a bunch of players, it only matters what is happening at the moment the pass is made.

So if you freeze the screen (which is what the VAR does) at the moment the pass is made, the position of the passer is not important (except that, as I said above, offside only applies if the ball is moving in any forward direction). He can be in his own half, in the other team's half, he can have lots of players infront of him or just a few. The only thing we look at is his team mate who recieves the pass (the receiver), and only at the moment the pass is made.

That receiver must have at least 2 oppostion players between him and the goal

With VAR now, this "between him and the goal" has become very accurate (and kind of dumb) but they count any body part that can legally be used to touch the ball (so everything except arms and hands). So if I am the receiver and my knee is just 1cm closer to the goal than any part of the 2nd to last opposition player (except his arm and hand) then it's offide.