Let’s say you have purchased a Traditional bow, then you have to determine how to aim to hit your target. There are several ways you can do this, and youtube has an endless array of videos which may help in this endeavor. But, for now, you can use the GAP method, or you can shoot instinctively, or perhaps a combination of both.
The most important step in all of this is to settle on a repeatable anchor, preferably with the arrow close under your eye so you can sight down the arrow to your target. (Consistency and repeatability is the key in archery).
The GAP method sights the arrow tip at full draw, relative to the target. You may think that in your line of sight you place the arrow tip on the bullseye and away you go, if only it were that easy. At various distances, you will have to place your tip either below or above, or sometimes on the bullseye, in order to hit the bullseye. The gap between your tip and the bullseye is why it is called the GAP method.
You can only work out what your gap is for each distance with much trial and error. Your anchor position is the biggest determining factor in trying to reduce this GAP. The reason the gap varies at the various distances is because of the trajectory or arc of the arrow flight and the distance to the target.
Other factors affecting this, to a lesser extent, will be the poundage of your bow, your arrows, arrow length and weight, the limbs of your bow and therefore the arrow speed when it leaves your bow among other things. See the diagram below:
Shorter Distance to Target
Longer Distance to Target
For example, an archer may be tip on at 25 yards (tip on means, the tip is on the bullseye when sighting down the arrow at full draw, so no gap), but the gap may be 10” below the bullseye at 10 yards. He then has to figure out what his gap is at all of the various distances in between to know where to aim, and when at his marker for a shoot, he has to be able to determine what the actual distance to the target is to know his gap.
Alternatively, you may prefer to shoot instinctively, which is akin to throwing a rock to knock a can off a fence post. You normally don’t put your eye behind the rock to aim, you just somehow sort of feel it and know where to aim.
Compound bows are another story altogether, and generally have sights through which you aim. But again, you have to judge the distance to the target to know where to aim. There are some classes of compound where you are permitted to use a range finder so you can determine the distance to the target, and this can be a good pathway, as a beginner, until you have a better idea of how to judge the distance.