Depending on the mileage and previous abuse of the diff, it might lock up well enough for you to learn the basics, or it could essentially be an open diff. If you have locking problems, you can buy a new preload shim and have it installed, this will increase the amount of torque required to 'break' the connection between the two wheels thus making the diff 'lock harder' (in reality, it is harder to 'unlock').
If you want to get a welded, get a welded. I'd suggest you drive on one first, they are kind of weird, and more often than not, it seems that people with little to no experience with them tend to do something derpy the first the time the road is wet or covered with sand or whatever.
Or you can get a 'real' differential like a 1.5 way or 2 way clutch type. Having personally DD-ed Opens, 2-ways and Weldeds, my preferred setup is probably the 2-way, just because it's like an on-off switch when properly maintained.
Oh well, you really should search for more information next time.
