Unless you're in combat or misusing your equipment, I wouldn't worry too much about accidentally spinning your turrets while getting out of the truck.
Two of my scopes have "tactical" (target) style turrets, and I've never had an issue with them spinning on me unintentionally (even in competitions). But, regardless, it's easy enough to look and see where you're at before you take the shot to make sure you aren't dialed to the wrong point… after all, you'll be adjusting before you take the shot in most cases anyway.
I have locking turrets on my very expensive Schmidt and Bender scope, and I almost never use the locking feature, because they've never spun on me unintentionally.
As for how they're used, here's the quick version (since I don't have much time to type right now):
1) Set it for a 100 yard zero. Scope elevation knob reads zero when dead on at 100 yards.
2) Determine my bullet's velocity using a chronograph.
3) Plug this information into a ballistic calculator (either online or the one I have on my iPhone) to develop a drop chart.
4) Range your target. Adjust your elevation knob (and potentially your windage knob) for the conditions and distance you're shooting.
5) Pull the trigger.
In my case my scope and reticle are both MIL system (rather than MOA). Either will work, but do yourself a favor and make sure your turrets and reticle are in the same system. I typically dial my elevation knob for the distance I'm shooting, and then hold the appropriate wind hold in the reticle (rather than dialing the windage knob). I do this because it's faster, and because wind changes quickly, often requiring different holds between each shot.