It has two inputs and two outputs. What you do with them or not depends on what your application requires.
You can make an RS232 adapter with two RS232 ports that both only support TXD/RXD, or you can make one port that supports RTS/CTS handshaking too, or you can choose to leave parts of it unused like on any other logic gate.
And like with any other logic gate, you must read the datasheet if an input can be left unconnected due to internal biasing, or does it require to be connected to some potential like VCC or GND.
Although if such a board already exists, consider if it is worth making it yourself or buying.