First one is a "safety notch"....meant to catch the hammer, should your thumb slip off while cocking the gun.
Second one is the loading/unloading notch. You can also note that due to it's shape, the trigger can not be pulled while the hammer is in this position....unless you use enough force to break the notch and/or shear the sear-edge of the trigger.
Third click is the latch (AKA bolt) being released back onto the cylinder via spring pressure.
Fourth click is the sear engaging the full cock notch on the hammer.
If you hold the (unloaded) gun up to your ear while you cock it real-slow, you'll probably hear 5 clicks. That's because most all SA revolvers are/were shipped slightly out of time....and the one's that weren't have gotten that way over the years.
If that is the case with yours, just look at the bright side.....
"They" say that 4-clicks spells C-O-L-T. So if that is true, I'm saying that 5-clicks must spell R-U-G-E-R. :wink: .
DGW