Wiring with crimp connectors

The easiest way to connect electrical wiring is to use quick crimp (QC) connectors

This type of connector joins wiring with mechanical force. The bare wire end is inserted into the metal barrel of the connector and the barrel is crimped, squeezing the connector barrel around the wire. The metal connector is covered by a tough plastic sleeve to protect and insulate the join.
The photos show how to join two wires using a butt QC connector, Also called a link connector.

Other types quick connector are shown below.
Bullet connectors are also used for connecting wires together, they have two halves, a male and a female, each is crimped to a wire then pushed together to join the two halves.
Female spades join wires to terminal lugs on batteries and connector tabs on electrical equipment.
Forks join wiring to terminals with fastening screws like those used in some solar panel junction boxes.