I have a 2000 camry and just the other day my a/c-heater fan will not work unless I put it on number four - will not go on until I put it all the way up to four. People tell me it is the sensor, but other tell me it is my fan motor. Can you help me and then tell me were in the engine is it so I can repair it.

You need what is called a blower resistor. On the outside chance could be a bad blower switch, but would do the resistor first.
The blower is working. Plain and simple there.