Serrano peppers are significantly hotter than a jalapeno pepper but not as hot as a habanero pepper.
You can use these green or let them ripen and use them when they are red. I find the red ones have a more fruity flavor. I use them when they are green or red.
I don’t see them red/fully ripe in the stores often so I grow my own and let as many ripes as I want.
Great to heat up some salsa like my Tri Pepper Salsa
You can make a really great hot sauce with the red serrano peppers by fermenting them. I’ll post my process to ferment and create a hot sauce in the future.