I would start by asking what actually is a foul? Or what is a foul play? So , foul is basically an unjust deed committed by a player for which there are yellow or red cards.

If we talk about the different types of fouls- they are as follows-
-Kicking an opponent.
-Tripping.
-Jumping into an opponent (like when you are going for a header)
-Charging into an opponent.
-Pushing.
-Tackling from behind.
-Tackling an opponent and you make contact with the player prior to making contact with the ball.
-Holding. (Source -www.ducksters.com)

Moving forward ,let’s talk about the yellow and the red cards. Yellow card is basically given to that player who misbehaves on the field. This, the yellow card is a warning card. The red card means the dismissal of the player from the field