I am entering the world of Raspberry PI. The reason I write, I require Raspberry connect the GSM / GPRS and GPS Fruit Adan (The 3 together) module. So far, I've only managed to connect the GPS and RPI or GSM / GPRS and RPI, previous TTL-USB wire. Is there any way to make the above?
The Pi has only one dedicated serial port (although there are software libraries to make soft ports). Your question is too vague to give a more detailed answer.
Even while most microcontrollers can "easily" emulate a serial port in software (that is a software uart) it will be probably more diffucult on the Raspberry Pi as it requires a very low level of programming. For some insight see How to get more than one uart interface
I maintain that it will be by far the simplest and easiest to attach multiple USB UARTs that will be recognised by the Linux kernel as separate devices and be adressed separately.