Some starter solenoids are mounted on the fender near the battery and some are on the starter itself.
Typically the ones mounted on the fender have two larger posts and one smaller post. For the larger posts: One connects strait to the positive post on the battery. The other connects strait to the starter. The smaller post connects to the neutral safety switch which connects to the start position of the ignition switch. Here is a diagram
. Make sure the solenoid is grounded good.
For the solenoid that is mounted on the starter: Connect the positive post of the battery to the large post on the starter. Connect smaller neutral safety switch/ignition switch wire to the smaller post.
Here is a diagram
if you have both solenoids
Don't forget to hook backup any other wires that were hooked to the positive side of battery/solenoid like alternator wire etc.