Everything around us is made from a variety of 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 (meaning that it doesn't react to form rust) easily. The bumpers are made from plastic because it is flexible, and the windows are glass.
The interior is made from leather or cloth for the seats, and plastic on the dashboard because it is cheap and easy to mould into the shape required. It will also have carpets on the floor and sound insulation.
There are many factors that must be considered when choosing a material:
Cost - is the material too expensive?
Availability - is the material available or is it difficult to source?
Properties - does the material have the properties required for the job?
Appearance - does the material look good?
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.