To use an abbreviation, type it and use the Expand Abbreviation command or the Ctrl+B key. The abbreviation is replaced by an expansion defined in the Abbreviations file. You can open the Abbreviations file with a command in the Options menu and add abbreviations.

Each line in the files looks like "abbreviation=expansion".
The abbreviations names can have any character (except perhaps control chars, surely for CR and LF), including high Ascii chars (accented chars).
Names have properties files limits: they cannot start with sharp (#) or space or tab (but can have spaces inside); and they cannot have '=' character inside.
Abbreviations names are limited to 32 characters. It is probably enough for abbreviations...

An expansion may contain new line characters indicated by '\n' and a caret position indicated by the '|' character. To include a literal '|' character, use '||'.
When expanding, the names don't need to be separated from the previous text. Ie. if you define 'é' as 'é', you can expand it inside a word.
If a name is the ending of another one, only the shorter will ever be expanded. Ie. if you define 'ring' and 'gathering', the later will see only the 'ring' part expanded.