OFFSIDE RULE!

Offside position.
It is not an offence in itself to be in an offside position. A player is in an offside position (not necessary offside) if:
he is nearer to his opponents’ goal line than both the ball and the second last opponent.

A player is not in an offside position if:
he is in his own half of the field of play or
he is level with the second last opponent or
he is level with the last two opponents

Offence.

A player in an offside position is only penalised if, at the moment the ball touches or is played by one of his team, he is, in the opinion of the referee, involved in active play by:
interfering with play or
interfering with an opponent or
gaining an advantage by being in that position

No offence.

There is no offside situation if a player receives the ball directly from:
a goal kick or
a throw-in
or
a corner kick

Infringements/sanctions.

For any offside offence, the referee awards an indirect free-kick to the opposing team to be taken from the place where the infringement occurred.

New International FA Board Decision 1

In the definition of offside position, "nearer to his opponents’ goal line" means that any part of his head, body or feet is nearer to his opponents’ goal line than both the ball and the second last opponent. The arms are not included in this definition.

New International FA Board Decision 2

The definitions of elements of involvement in active play are as follows:
Interfering with play means playing or touching the ball passed or touched by a team mate.
Interfering with an opponent means preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or movements or making a gesture or movement which, in the opinion of the referee, deceives or distracts an opponent.
Gaining an advantage by being in that position means playing a ball that rebounds to him off a post or the crossbar having been in an offside position or playing a ball that rebounds to him off an opponent having been in an offside position.

Bit confusing isn't it! All will become clear over the next few weeks.