There is nothing much to say about ASCII file transfer, just press AltT and choose the file you want to send. Pressing Help gets you to the Help screen, so you can change the delay between characters to a different value during an upload (this is useful with VMS which normally has a lot of trouble with the first line sent). The transfer can be interrupted at any time by pressing A. Normally some experimentation is needed to find the shortest delay time for your system. You can use a character translation table to map incoming characters to Atari characters.
To receive files use the file capture function. A translation table is used in the same way as with sending files. When file capture is in effect the characters are displayed as they will be saved.