As far as talking doing it the regular way:
First thing you need is a device that adds a "PC style" serial RS232 port to the Atari 8-Bit. There are plenty of ways to do that. A SIO2PC interface can be considered as being one.
Next, you need a driver on Atari 8-Bit that adds an "R:" handler to HATABS. Just like you use "D:" to access a disk drive, or "P:" for the printer, you need an "R:" to access the serial interface but it has to be loaded/installed by yourself. Since the SIO2PC hardware is very similar to the RVerter interface you may try the RVERTER handler (It's on the IceT ATR 2.74 posted a little while ago, just to name one location).
Buy/make/borrow/steal a null-modem cable (or correctly wired break-out box). In case you need it, wiring is on my site:
http://atari.mixinc....uts/pinouts.htm
Connect PC and Atari with the null-modem cable.
Load a terminal on both systems. Config as ASCII, 9600 baud, No parity, 8 bits, 1 stop bit (in many cases this is the default).
Check if you can send text back and forth between the 2 systems by typing characters in the terminal screen. If you see strange characters when typing, double-check your baudrate setting.
Once you can get this to work it's time to move to step 2...