Copper alone was not much good for making swords because it is too soft. Copper swords kept bending. You can’t fight with a bent sword.
Tin on its own was too brittle. Tin swords would break.
But adding a little tin to copper (to turn it into bronze) made swords much stronger without making them brittle. They would still bend if made too big, so Bronze Age swords were little more than daggers.
Iron swords were best of all.
The Bronze Age came before the Iron age because copper and tin can be smelted (extracted from their ores) at temperatures obtainable from an ordinary wood fire.
The Iron Age came later because it takes much higher temperatures to extract and purify iron.