Can ayone help me out I have 2 usb's on my laptop one controls the printer and the other controls my mouse, However I would like to add another device on to this (digital Camara) how can I add 3 devices to 2 USB's

you can buy a USB hub from most computer shops for very little. this will plug into one USB port and expand it to two or four (sometimes more) USB ports.

Can I just unplug one device and plug the other one at a time in the same usb plug

You could use the printer one and see if it doesn't create a conflict. If you've installed your camera software it should automatically pick up when you plug the camera in.