Peoplel are sending me very imp. faxes and idk how to recive it..

If your printer has FAX capabilities. Good way to tell is if you have a phone number pad on the front of your printer.

You must have this connected to a phone line for it to receive a fax.
Setup the fax application through your installation CD that came with the Printer/fax machine. Often you set the fax machine to pick up after so many rings. This allows you to leave the printer/fax machine on and gives you time to answer BEFORE the fax machine does. If uncle Bob or Aunt Susie should call to say Hi!

Basically what is happening:
You turn on the Printer/Fax machine it sits idle waiting for a phone call.
Someone now sends you a fax using your phone number.
YOUR printer/fax machine is sitting there listening for the phone to ring.
Lets say you have your printer/fax machine setup to answer after 5 rings.
After 5 rings, your Printer/fax machine will pick up and listen for signal tones from the the other machine. If it gets these, it will "handshake" and send a confirmation fax tone. Then the data will be transferred and printed out on your machine or held in a fax program for you to print or save later.

It is critical that you do not pickup the phone too early or the two fax machines trying to communicate will fail.
If you do this, you will hear an awful squeal and a serious of tones.
You can often hang up quickly and the two machines will transmit again the handshake signals and resume business as usual.

Short answer:
Two fax modems are talking to each other over your phone line to transmit data.

Good luck!
and hope this is helpful.