ok, i have an 84 and an 86 4x4 Blazer S10. Both have shifters on the floor and have indicators. There are 4 positions:
(1)2 Lo - closest to the front of the vehicle
(2)4 Hi - shift to and from 2 lo at any speed, just not on pavement and especially careful with the wheels not straight.
(3) Neutral -this position is for emergencies like winching and towing ect...I am neurtal towards everyone reading this!
(4) 4 Lo - this position requires caution. Always have your main trans in N (both mine are automatic). When you shift, do it continuously from 4 hi to 4 lo as not to grind. Do not stop in the 3rd position.
there are also lights on the left side of the shifter to indicate if the differential is engaged. the lights often burn out and the diff often sticks in 4 high. If this happens, just step on the brake (preferably when the vehicle is on a slight incline) move the shifter if nessicarry. The shifter works on a 12 volt and the actual locking in place of the front axle is hydralic (I think!)
get out there and get stuck! make sure both axles are spinning!