Trade and win
Master this and many more motifs
Sometimes a piece can be attacked and protected multiple times. A sequence of captures can then happen on that square. Such a sequence of captures is called a "trade".
It is important to look at these possible trades and determine their outcome. They can win material, lose material, or exchange equal amounts of material.
Black can win a rook by trading on d2: 1...Qxd2 2.Qxd2 Rxd2
We say that the Rook on d2 is "insufficiently protected".
Sometimes there are multiple possible captures on the same move. In most of these cases, it is sufficient to calculate the capture with the least-valuable piece capturing first.
White can win a knight by trading on d5: 1.Nxd5 Nxd5 2.Qxd5
Capturing with the queen first would not be a good idea, after 1.Qxd5? Nxd5 2.Nxd5 White would have lost a queen for two knights, a material equivalent of losing three pawns.
After each capture, calculate the sequence of trades on that square.
Remember that you are not forced to make any subsequent captures. If the subsequent capture would not gain further material, it might be better to stop trading and play a different move (especially if subsequent trades would lose material).
With some practice you will be able to spot winning trades very quickly and analyze more complicated trades with confidence. Captures and trading are the fundamental ways to win material and are the basis for learning more advanced tactics.