Finishing Phase
Before the attacker gets into shooting range, his main job is to hang onto the ball. As long as he has possession of the ball, the other team cannot score, so it is to his benefit to do what needs to be done to keep possession of the ball - but only until he gets into scoring distance of the opposing goal. Once in a good shooting position, there is little risk in taking a shot - and a lot of potential benefit to be gained.
While this is obvious to adults, it is not always obvious to children. Many children are very literal-minded. If the coach tells them to make sure to always try to hold onto possession by passing the ball around to open teammates, it is not uncommon to see them pass the ball around in front of the goal - and never attempt to put it in the net. Furthermore, if the coach spends lots of time on drills which have them carefully placing their balls on the ground, then backing up to take a net-breaking shot on goal, they will often pass up open chances to simply roll the ball into the goal in favor of trying to score "the way that coach taught us". As a result, it is very important to explain to young players when it is okay to take risks, and when it is better to play safe. It is also important to give them permission to score (which also means giving permission to miss, because the easiest way for a new player to avoid getting yelled at if he misses is to never take a shot).
The first thing to teach the attackers is that very little actual space is needed to get the ball around a defender or goalkeeper so that it can roll into the net. The ball just needs to clear the legs of the defender by an inch or less on either side. It is important to illustrate this idea to young players, so that they understand that it is possible to score goals in very tight quarters - and that they should try to do this.
The second thing to teach young players is that, to score goals, the best place to send the ball is to the place where it will be hardest for the defenders to get to it. Usually, this means that the safest place to send the ball is to the corners of the goal. However, if the middle of the goal is wide open, it is fine to send the ball there.
The third thing to teach young players is that you want them to score a lot of goals - and the very best way to do this is to pass the ball into the net as soon as they see an opening to do this, because passes are more accurate than shots and are easier to get off quickly. As a result, players should be encouraged to score goals using simple passes with the inside or outside to put a MOVING ball into the net. The coach should strive to create game-like situations in practice. As a practical matter, no defender or goalkeeper is going to allow your attackers to put a ball down in front of the goal, back up, and then run at it to blast it into the net. Scoring drills which involve long lines and stationary balls do a poor job of duplicating game conditions, and do not tend to create players who are comfortable in scoring goals with a moving ball by putting it around the feet of vigilant defenders.
The fourth thing to teach young players is when and where to take a shot. In other words, to introduce them to the concept of when they have entered "scoring range" - and should start to think about taking a shot.
Finishing Angles
For players and keepers to understand shooting angles, one of the easiest things to do is to purchase two long pieces of brightly-colored plastic rope. Yellow ski rope is perfect. Tie one end of one rope to a goalpost, and one end of the other rope to the other goalpost (if you only have one rope, tie both ends to the posts). Then, put an attacker on the field in front of the goal and intersect the ropes so that the attacker is standing on the intersection. Now, take the goalkeeper and put him between the ropes so that he can touch the rope on either side if he dives to that side. Show the players out in the field that they can get a pretty good idea of whether the goalkeeper is in proper position by just holding out their arms so that their hands are pointed at each goal post - and seeing whether they think that the keeper is centered on the angle and is out far enough. Initially, put all of the players behind the attacker, so that they get an idea of what you are doing.
Next, divide the players so that half are behind the keeper and the other half are behind the attacker. Set up sample angles, starting at the middle of the goal and working towards one side. Put a cone where the keeper needed to stand to be positioned properly. Once you get to very narrow angles towards the sides, have the groups change places to see things from a different point of view.
From this angle-mapping exercise, the players will see quite easily that the best approach on goal is dead-on towards the center of the goal. This approach makes the job of the keeper more difficult, because he must come very far off of the goalline in order to be able to cut down the shooting angle of the player. Because he is so far out, if he misses, the attacker has an easy shot on goal. Once attackers have learned to accurately chip the ball, it becomes even easier to punish a keeper who comes off his line - by simply lifting the ball over his head so that it can roll into the net behind him. Although you probably won't work on chips until later, it can be fun to point this out to the players to get them started thinking on scoring opportunities. Another thing that the players will learn from this exercise is that, once the ball can clear the inside of the near post (even if they are coming in from an angle), the keeper has so much territory to cover that it becomes much easier to slot the ball around him.
With this basic information on angles, they are ready to start to learn how to finish. This is a life-long process which involves some rapid processing of information, so miscalculations are inevitable (even among pros). Even the very best strikers in the world, who are playing at the highest levels, score only about once out of every six tries - which is one of the reasons that it is so important to encourage players not to get discouraged if the first few do not go in.
There are 3 basic finishing options which they will need to learn. These are central finishing, and angle finishing to the near and far posts.