AT ALL LEVELS: If posted goals, permanent or temporary, are used, they MUST be properly anchored so that they don't fall. People (usually boys and girls) have been injured and killed by goals that fell on them. Players must be sternly warned not to hang on goals nor nets.
Okay, let's get to the bussiness of Law 1.
For the beginning coach and parent, just remember a few things (you can get all the "official" stuff at FIFA.com).
First, all soccer fields must be longer than wide. The sizes vary with the divisions and to get your relative size at your club, get hold of the official in charge of the fields. Even with that, some club officials get the sizes incorrect. Look at the web sites for your club and parent organizations and you'll find it.
An example of field sizes for the various levels is at the United States Youth Soccer Association web site, USYSA.com.
Above is a field with all the bells and whistles for markings. At the U6 level, only some of the markings will be there.
You can see the outline of the field. There will be two goals, one at each end on the lines that run the width. Those lines are called GOAL LINES. The goals should be right in the middle of those goallines. At U6 you'll have no other lines around the goal area.
In the middle of the field is a circle. Later in the Laws we talk about free kicks. In soccer the opposing team players must be at least a certain distance from the player taking that kick (with minor exceptions around the goal, when the distance between the kick and the goalline is less).
At the upper divisions that distance is 10 yards, while at U6 it is usually 4 yards.
At kickoff (start of the game, after a score and start of the second half), the opposing team has to be that distance away. To make things easier, that distance is marked from the center kickoff spot. At kickoff, the players must start on their own half of the field and the arc marks that distance on their own half. Put the two arcs together and you'll see the center circle.
The line in the middle of the field divides the field in half and is called the HALFWAY LINE.
There are some quarter arcs in the corners and those are there to mark the spot a corner kick (later in the Laws) is taken from. These are called CORNERS.
For U6, that is all you need for field markings. You may put plags in the corners to mark them (I prefer them), but you don't need them. If you use flags at ANY level, they must be five feet tall for safety.
At the U8 level (six and seven year olds and in USYSA), another marking is added. It is called the GOAL BOX. It is used for marking the area the ball will be kicked into play from, after the ball crosses one's own goal line by the other team without scoring (kicked into the goal).
If you look at the drawing above, that will be the smaller box by the goal.
Starting with U10 (eight and nine year olds) the final box is added. It is called the penalty box and is the larger of the two boxes by the goal. At the U10 level we start playing with a goalkeeper (Not goalie, please; that is for hockey games). That bigger box marks the area where the keeper is allowed to use the hands to handle the ball (the only player allowed to do so with certain criteria). Later you will see why this called the PENALTY BOX.
Other than four flags in the corners, that is the soccer field. The dimensions for lower divisions will vary to accomodate the smaller player, but other than that we have covered the field.