You will have two wires to the starter. One is the heavy gauge wire that actually turns the starter. It bolts to the large post on the starter.
The other wire is smaller, connected to the smaller terminal on the starter and is energized from the ignition switch.
When the switch is turned to the start position, the solenoid picks up and makes up the contacts that connect the large wire to the starter windings to turn the starter.
If you don't have a service manual, you should.
It has the wiring diagrams you need to work on the electrical system.