If you’re comfortable with the language of schemes and representable functors, you can find a nice introduction to Grothendieck topologies here: Notes on Grothendieck topologies, fibered categories and descent theory, by Angelo Vistoli.

If you’re comfortable with the language of schemes and representable functors, you can find a nice introduction to Grothendieck topologies here: Notes on Grothendieck topologies, fibered categories and descent theory, by Angelo Vistoli.