This is what I know about steganography. Its an old encryption method. The process is you hide a data into another data. Meaning you hide a text or a message into another image, file, message, video etc.

And after a short research I found out that you can encode via this method in a few ways. such as:

-Physical encoding.
Writing a message and hiding it in the messengers body, writing it in invisible ink, writing and hiding it with stamps, writing in Morse codes etc are physical typology of steganographic encoder.

-Digital messages.
You can hide a mesage or anything in a corrupt file, another image, noisy pictures grainy parts, audio files, sound templates etc and every other kind of data that is available..

-Digital text.
This is the most interesting encoding method. Like writing as the same color as the background, using unicode for ascii, using hidden charecters etc and hiding a message.

there are many many other types of encoding options... just do a short research in Wikipedia and you will leearn all you need to know.