I need help with Mixin

Hello.

I recently tried to use Mixin to inject my events into minecraft etc.
And im finding it quite hard to even configure it.
I’ve done the injecting part, I’ve done all of that.
But I just need help with getting it to start, is it to do with the build.gradle? #
(I did try to use --mixin but that didn’t work as an argument ;-; )