Two wires and a wire connector
One thing I learned as an apprentice, was to make sure the ends of the two wires were flush before starting to screw the wire nut onto the pair.
When the pair started to twist at your fingers that are holding the wire, It is probably a good connection
Test your connections
When you finished screwing the wire nut onto the pair of wires, always give them the “pull” test to be sure. if you can grab the wire nut with one hand, and the wire with the other and make an attempt to pull them apart, they should all be firmly set. If one wire comes out of the wire nut, it would have given you problems
If a wire connection is not so good, it can cause arcing inside the wire nut, and build up A LOT of heat really quick and give you some real headaches when you go looking for the problem. A loose connection can also take days, or even months before it starts to cause problems.
About 3 months after we had moved into our current house, the fuse for the water heater blew, and it turned out to be a bad connection where the wire went into the water heater. The wire was arcing against the cover plate because the casing on the wire nut had melted.
So be safe, and test any electrical connections you make.