To harvest fresh chillies cut or pull off the mature fruit while it's still shiny and plump.
You can harvest the first chillis green once they reach full size. Or you wait until they turn red, or whatever colour they are supposed to turn.
If you plan to dry them for chili powder or flakes, you can even leave them on the bush until they shrivel up and dry.
If you pull it off, pull it upwards, exactly opposite to the direction in which it bends down. Then it should snap off at the joint, without breaking off the whole branch. Otherwise just snip them off.
The fruit will last in a sealed bag in the fridge for up to a week.
You can dry it in the dryer or sun dry it, you could also just string it up and hang it up to dry in an airy spot.
Pound it to flakes or put it in the blender to make cayenne pepper and chili powder.