Neither the touchpad nor the pointing stick on most laptop computers is a really good substitute for a traditional computer mouse or trackball. Unless you're using the laptop in a very limited space, an external mouse connected to the computer's USB or PS/2 mouse port is easier to use than the internal pointing devices.
To connect a mouse to a PS/2 port, plug it in before you turn on the computer. You can connect a USB mouse at any time. Windows should automatically detect a new mouse and run a configuration program that assigns commands to the buttons and allows you to choose other options. After the configuration is complete, Windows uses that configuration whenever a mouse is plugged into the computer. On most computers, the external mouse and the internal touch pad or pointing stick (or both) work at the same time, so you don't have to tell the computer which device you want to use.
If you travel with your laptop computer, you may want to use one of the smaller mice that take up less space in your computer bag. Look for a mouse with a model name that includes the words compact, notebook, or mini. If you travel by air, don't use a wireless mouse; most airlines won't allow you to use radio transmitters in flight.