ON the 5425, there is a Range lever with three ranges, A, B, & C. You must stop and use the clutch to change ranges.
There is a Gear lever with four gears, 1-4. You must clutch when shifting gears, but this can be done ''on the go', NO need to STOP as with the Range shifting.
The PLUS is a HI-LO feature. On the side of the gear shift knob are two buttons, top one has a Rabbit, bottom one a Turtle. While in any Range or Gear, you can push the Turtle button (without clutching) and drop down about 1/2 as much as compared to shifting the Gear shift lever to the next lower gear. Push the Rabbit button (without clutching) and you up shift back to the gear you are currently in. So the 12 speeds of a 5425 become 24 and since you have a Reverser, 24/24. The 5M series you can get four Ranges x four Gears = 16 speeds and with HI-LO, Reverser = 32/32
Reverser is a lever that allows changes from forward to reverse and reverse to forward in any range/gear without clutching. It can make for some very FAST backing, be careful!