By running a lot, eating right, practice skills like heading the ball, dribbling, passing, etc. If you have a love for it, it isn't so hard! Like many sports, soccer players work out in the gym,...
The basic answer is no, but traditionally, managers have been players. As with any job you need to understand the basics before you progress to the bigger picture, and this experience may be acquired...
Yes you have to play for a soccer club or team to go into big games that are known like at a stadium. But you certainly don't have to be in a club to play a game of soccer with your friends!