what is the differance between a charging and blocking

In a charge, the defensive player has to have established legal garding posistion (both feet inbounds, both feet on the floor, and facing the opponent being guarded), legal guarding posistion can be kept, if the defensive man is not moving toward's the offensive player, and remains inbounds. Any contact to the torso while the defensive man has legal guarding posistion is a charge.

any other contact where the defensive player does not have posistion or if his arms are parallel to the floor, and the contact is made on the arms, is a block

Let's back up a minute here. In terms of the infamous "Block/Charge" ref18 gives a decent overview of the basics, but you should also keep in mind that the signal and call for "Block" can also be used for illegal screens, and other illegal contact away from the ball by both offense and defense.

Here's the exact wording from the official rule book for HS, see 4-7-1 and 4-7-2. "Blocking is illegal personal contact which impedes the progress of an opponent." "Charging is illegal personal contact caused by pushing or moving into an opponent's torso. etc etc" As the definition of charging progresses, it becomes clear that "charging" means pretty much the same thing as "player control foul." Blocking is illegal screens, illegally stepping into the path of the dribbler, stuff like that.

Technically, charging also includes a defensive player who knocks over a legal screener. "Pushing into the torso" of the screener is charging, even though most of us don't call it that way in order to avoid confusion. Charging isn't limited to the PC call.

mmmmm....I dunno about that

A1 releases the ball on a pass then runs into B1.

A1 sets a legal screen and B1 runs through him.

Both charges, no?

Pure definition
 

All a PC Foul is, a foul with a player in possession of the ball or an airborne shooter. Charging is really a separate foul. But the word "charging" is usually associated with a PC Foul.

Peace

Here are the rulebook definitions
 

NCAA Rule 4

Section 7. Blocking
Art. 1. Blocking is illegal personal contact that impedes the progress of an opponent.

Section 8. Charging
Art. 1. Charging is illegal personal contact by pushing or moving into an
opponent’s torso.