Engine doesn't turn over easily

What switch would it be? And what are all components in the starting circuit? What is the solenoid? and are there any tests I can do to determine what it is?
Solenoid is on drivers side fender well...small metal thing with wires about 1.5" X 2"

Just really check everything you can. ...battery cables....etc.
Any loose wires? Very much messing around and I'd disconnect the battery.

Jeff