It means that you can not score directly from the kick another player has to touch the ball for it he/she is able to score
An indirect free kick must be touched by another player before it goes into the net to count as a goal. A direct free kick does not.
No, if it's a defender against an attacker, it is a penalty. "Foul" is a term used to describe direct free kick offenses. Those are automatically promoted to a penalty kick while in the penalty area.
The kick off is neither direct nor indirect, they are three different restarts. A goal may be scored from a kick off.
A direct free kick is a direct shot at goal, which has a chance to be converted. An Indirect free kick is usually taken with an aid or a pass and is given in less dangerous positions