CAD stands for Computer Aided Design, whereas CAM stands for Computer Aided Manufacture.
CAD is used for displaying and editing designs on the computer. Calculations can often be made. CAM uses a computer to control a manufacturing process.
CAD can be used for interior design work, such as arranging furniture in a room. This can be viewed from a number of different angles.
The arrangement can be changed on the computer and 'tested' without needing to move actual furniture around.