I have copies of several books/publications on my web page at
https://www.navy-radio.com/manuals-ttycorp.htm#books

If you have recently acquired your first Model 15 or Model 28, for example, then TTY for the Deaf is a good background resource (hat tip to Jim Haynes)
https://www.navy-radio.com/manuals/tty/jh/ttyman1/ttd.pdf

If there are other links I should include, please let me know.

Cheers,
Nick England K4NYW
www.navy-radio.com