Everything around us is made from different materials. The properties of a material must be considered to establish how suitable it is for the object being made; for example, you wouldn't make a teapot out of chocolate!
A car is a good example to look at because it is made from many different materials:
The exterior of most modern cars is made from aluminium because it is lightweight and doesn't corrode easily. The bumpers are made from plastic because it is flexible, and the windows are glass.
Gold is an excellent material for making jewellery. It has a beautiful appearance but is expensive because of how rare it is. Gold is a soft metal and, because of this, it is mixed with other metals to make it a bit more hardwearing. 9ct gold contains about 38% gold and the rest is copper and zinc, which make it less expensive but more hardwearing.