Go stones do not have values, so the only way one move can be better than another is efficiency: how much it achieves per stone. That is what shape means.
The empty triangle: the shape to avoid
Three stones forming an L with the fourth point empty. It uses three stones to produce seven liberties, where a straight line of three produces eight. It also makes poor eye space. It is the classic beginner shape and almost always there is a better alternative one point away.
There are exceptions — sometimes an empty triangle makes an eye or captures something — but as a default, if you are about to make one, look for another move first.
The tiger's mouth
Three stones in a V with a gap at the mouth. If the opponent plays into the gap, you capture immediately, so the shape defends the point without occupying it. It is one move more efficient than simply connecting, and it frequently becomes an eye later.
The bamboo joint
Two pairs of stones with a two-point gap between them. It cannot be cut: if the opponent plays at one connecting point, you play the other. It is the standard way to connect two groups without spending a move.
The one-point jump
A stone two points away from your own along a line. It is almost never cuttable in open positions and it covers ground twice as fast as a solid extension. The saying is that the one-point jump is never bad — an exaggeration, but a useful default when running or extending.
Hane and the head of two stones
A hane is a diagonal move at the edge of an opponent's stones, wrapping around them. Haneing at the head of two stones — playing diagonally at the end of an opponent's two-stone line — is one of the strongest local moves in go, because it forces them into inefficient shape while you gain.
Hane at the head of two
If your opponent has two stones in a line and you can play diagonally at the end of it, look hard at that move. It is correct far more often than not.
Thickness and where to use it
A wall of strong stones is called thickness. It is not territory and trying to turn it directly into territory wastes it. Thickness is for fighting: it makes nearby battles safe for you because your stones already have liberties and eye shape.
The standard advice — do not play close to thickness, including your own — follows from this. Playing near your own wall means your stones are doing the same job twice.
A shape checklist
- Am I making an empty triangle? Look for an alternative.
- Can I connect with a bamboo joint or tiger's mouth instead of solidly?
- Is a one-point jump available instead of a slow extension?
- Does my opponent have two stones in a line I can hane against?
- Am I adding stones near my own strong group for no gain?
Running this list takes seconds and improves most moves, which is exactly why stronger players appear to play fast. They are not calculating more; they are recognising shapes and trusting them.