writing code for alternate glyphs


Hi everyone. I'm making my first font and it has a ton of ligatures. I have six versions of some ligatures. Now I'm beginning the proces of getting them to work with code, though I've never written code I'm learning it as I go, with this font.

My question is about the difference between stylistic alternates en stylistic sets. What is the difference exactly??
The manual says this about stylistic alternates... or contextual alternates

Alternate Substitution
Alternate substitution replaces a glyph with one of the glyphs in a predefined
list of alternatives. The application that uses the font is expected to
decide which glyph to choose. A good example of this lookup is to provide
several versions of some glyph, like the ampersand. Another application is