What does GD GP and SO mean in soccer?

It stands for goal difference. Goals scored by the team count as positive points and goals scored against count for negative points. It is only used in the event of a draw at the end of round robin play to determine which team moves on. Other than that it does not count towards the point like wins, or draws do. In other Words, GD means goals difference ( lets says your GF is 30 and your GA is 10 then your GD will be 20 )

The GD is better when its a large number. EXAMPLE: if two teams are tied with lets say 92pts at the end of the season then the next thing that will decide who is champion is whoever has the higher GD