Each pattern can be linked to a kit.
By loading a kit into a pattern, or by saving a kit to a slot, you link the current pattern to that kit.
Multiple patterns can be linked to the same kit (when you want multiple patterns to share sounds, performance macros). You can load a kit into a pattern or you can switch to a pattern, tweak/load sounds and then save as a kit.
You have 128 slots for kits in a project, so if you want, every pattern can have its own kit.
If you overwrite a kit slot (=save a kit onto an already existing kit slot), you ofc change all the sounds, fx track parameters, cv track, performance macros on all patterns linked to that kit to the now saved settings.
A kit contains the four sounds on the four synth tracks, cv track and fx track parameters and perf macros.
The sounds can ofc also saved individually, a kit is just a collection of all those things played by a pattern.