What is a Wire-nut or Marr Connector and how are they Installed?
A twist-on wire connector is a cone shaped threaded plastic item that's used to connect wires together. "Marrette", "Marr connector", "IDEAL Wire-nut" are trade names. You'll usually use a lot of them in DIY wiring. They look like this:
In essence, you strip the end of the wires about an inch, twist them together, then twist the connector on. While some connectors advertise that you don't need to twist the wire, it doesn't hurt. The Ideal wire-nuts specifically state you don't need to pre-twist. The spring inside helps make the connection and if you properly twist the wire nut until the insulated part of the wires start twisting, then the stripped wires inside the nut are also twisting. They work pretty well.
There are many different sizes of wire connector. You should check that the connector you're using is the correct size for the quantity and sizes of wire you're connecting together. Never exceed the number and gauge or wires specified by the manufacturer for a wire nut.
After twisting the connector on, give each wire a tug, and make sure that nothing is loose. Some people wrap the "open" end of the connector with electrical tape. This is probably not a good idea - the inspector may tear it off during an inspection. It's usually done because a bit of bare wire is exposed outside the connector - instead of taping it, the connection should be redone.