2 feet are coils, and the other 3 feet have 1 only for common terminal, 1 only for moving on, 1 for moving off. The relay is equivalent to a single-pole double-throw switch. There are three pins that control the external circuit. When the control current is not passed, the middle pin is connected to a left pin. When the control current is passed, the middle pin is connected to the right pin, and the relay's pull-in is to make current act on the electromagnet,

Since this current is not small, the I/O port of the microcontroller alone is not enough to make the relay pull in. A driver should be added. Then the microcontroller uses the I/0 port to control the drive, and then the drive circuit outputs enough current to make the relay pull in. combine.
There are 3 basic forms of relay contacts:
1. The two contacts of the moving type (normally open, H type) coil are disconnected when the coil is not energized, and the two contacts are closed after energization. Indicated by the letter "H".
2. The two contacts are closed when the coil is not energized, and the two contacts are disconnected when the coil is energized. Indicated by the letter "D".