Maxims MAX232 is one of those wonderful components that solves so many signal conversion problems.
This chip converts RS232 signal voltage levels to TTL voltage levels and visa-versa.
Hence if you need to communicate to your PC through it's serial port (COM1 or COM2) then this is the chip that can perform that function. If you have a microcontroller circuit, or a phone, or a calculator that requires a PC connection then this is the chip that is needed to make that communication happen.