There are many thing you need to play soccer. The first and probably the most important thing you need is a soccer ball. You also need shin guards to protect your shins (obviously). You also need cleats or you will probably slip. A team uniform would help you identify the players on your team.
In pro soccer there are 11 players allowed on the field including the goal keeper. Managers usually do a line up of 1-4-4-3. 1 goalkeeper, 2 full backs, 1 left back, 1 right back, 1 central mid, 1 left mid, 1 right mid, 1 right wing, 1 left wing, and 1 striker. If some players are tired or injured the manager can play a sub for the player. But you can only sub 3 players per game.