The starter solenoid is a relay switch that contains 2 circuits and has 3 or 4 wires connecting to and from it. Two of these wires are heavy gauge, and the remaining are smaller gauge. The two heavy gauge wires are connected to your starter and to your battery. The remaining small gauge wires are connected to the small terminals on the starter solenoid and lead to the ignition switch and to the common ground. If your starter solenoid only has one small wire or terminal, the ground is through the solenoid’s mounting bracket.
To measure AC voltage for example on your engine’s stator, you first locate the two wires coming from the stator. Turn your DMM to AC Voltage. Place the red probe onto one of the wires, and the black probe on the other wire. You should read about 24 to 30 VAC.
The basic components in a hydraulic system are:1.) Reservoir 2.) Pump 3.) Valve 4.) Piston or Motor
This article serves as a basic introduction to what is possible with hydraulics for your garden tractor. There are a wide variety of pumps, valves, motors, hoses, etc. I hope this article inspires you to research more of what you can do with the physics of fluid.