The inventor of the PC Modem in 1977 what does this device do?

You use a PC modem to connect to the internet. It will generally connect through to your Internet Service Provider (ISP).

It allows either one computer - or a group of computers which are served by the same router - to connect to other systems.

Its designed purpose is a) to send information outwards and b) to receive information inwards and to do both of those things at the same time.