While patterned on Men's Lacrosse, Women's Lacrosse is actually a derivative, non-contact sport that was created in England and came to the US in the 1920's.  The focus of both games is to out score the opponent by shooting the lacrosse ball into the opponents' goal.  Below are some of the rules specific to Women's Lacrosse as played by Norwood Girls Youth Lacrosse program.

Quick Guide:
 
Checking & The 3 second Count: 

Grades 3/4 & 5/6: No stick checking is allowed at the Grades 3/4 or 5/6 level.    However, in these divisions, if the defender is in a position to check and holds that position for 3 seconds- as determined by the umpire-  the defender gains possession of the ball. The umpire will count the seconds.

Grades 7/8:  In this division, modified checking is permitted. Modified checking is defined as the defender striking the head of the stick when the entire stick is below shoulder level.  The defender must use a downward motion away from the other player's body.

Stick-to-stick contact does not violate the checking rule if the attack player -- not the defender -- initiates contact as in the following situations:

A) A defender holding her stick in good defensive position forces the attacker to cradle into her stick causing contact.
B)  A defender with her stick up in an attempt to block or intercept a pass or shot causes the attacker to make contact while in the act of passing or catching the ball.

Fouls: There are two types of fouls- Direct Free and Indirect Free.  In a direct foul they have the ability to shoot on goal.  Indirect they may not.  In all fouls, the fouling player is placed 4 meters behind the fouled player and the area in front of the fouled player is clear or “free”.
 
Shooting Space: Is the space in front of the ball carrier to the edge of the crease.  A defender who is not within a stick’s length of the ball carrier may not block the ball carrier or enter the “free space to the goal“ when that attacker is in position  to or in the act of shooting.  Violation results in a Direct Free position.
 
Crease Violation: Only one player may be in the goal crease at the time (usually the goalie). Violation creates a possession turn over to the opposing team.

Out of Bounds: Fields are lined with a fixed boundary marker.  There are two separate rules that govern out of bounds that depend on the type of play occurring.

Passing Plays:  If an offensive player attempts to pass the ball to a team mate and it goes out of bounds, the other team is awarded the ball.

Shots on Goal: If a shot on goal goes out of bound- whether it was deflected or not- the player closest to the ball at the time it goes out of bounds- from either team-  is awarded possession of the ball.
 

Here are links- some with video- to better explain some of the rules! 

Founders Girls Lacrosse Leagues

2014 Women's Rules Changes 

2014 Women's Rules Points of Emphasis

Shooting Space Explained