Tactics are the lifeblood of chess. While strategy is your long-term plan, tactics are the short-term tricks that actually win pieces. If you master these four patterns, you will stop blundering and start spotting winning opportunities in almost every game.
A Fork happens when one of your pieces attacks two (or more) of your opponent's pieces at the same time.
A Pin happens when a piece cannot move because a more valuable piece (like the King) is standing behind it.
A Skewer is a "reverse pin." You attack a valuable piece, forcing it to move away, which exposes a piece behind it.
A Discovery happens when you move one piece out of the way, unleashing an attack from a piece standing behind it.
Pattern recognition comes from repetition. You can try random puzzles, or take a structured course to learn them all.