Scale armor is like a secret suit of armor that warriors wear under their clothes to protect themselves from enemies. Imagine a coat made out of hundreds of tiny fish scales that are linked together by metal rings or leather. When the warrior gets hit by a sword or a spear, the scales of the armor will spread the power of the attack out so it won't hurt as much.
It's like when you poke a balloon with your finger, the balloon pops, but if you put lots of layers of tape on the balloon, it's harder to pop the balloon. That's basically what the scale armor does, it makes it harder for attacks to hurt the warrior wearing it.
Scale armor is made from different materials such as metal, leather or even fish scales. The scales are usually arranged in little columns or rows that cover the warrior's chest and back to keep them safe. Warriors wear scale armor because they want to stay alive and protect themselves from harm when they go into battle.