Metals are not usually very useful in their pure form – they can be too soft, too hard, or too brittle (break easily). So they are made into an alloy by adding other metals to them in different quantities. Bronze is an alloy of copper and tin, while brass is copper and zinc. The choice of which kind of metal to use for an object depends on what you want to make. You would not make a sword blade out of gold, for example – it is too soft.
Metals also change their characters when they are heated or hammered. Steel and silver, for example, can be beaten or rolled to make very thin sheets. This makes steel very good for making things like armour. It is very strong, but a little can be made to go a long way so it is not too heavy to wear.