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.
The RS232 serial port protocol (v.24) states -15v to represent binary 1 and +15v to represent binary 0. For TTL communication this is incompatible since TTL uses 0v to represent binary 0 and +5v to represent binary 1. MAX232 chip converts serial signal voltage levels to TTL standards, and also vias versa. It therefore has a driver and a receiver to perform this function.