Hi Fronteragirl. Autoloclikng hubs means that when on an "A" series you select 4wd, as the wheels first turn forwards the hubs engage giving 4wd in forward motion. If you then reverse, the hubs momentarily dissengage and then engage again in reverse motion. This can have a detremental effect if stuck in mud and you are rocking back and forth to free yourself as the constant engaging and dissengaging has a snatch effect and can damage the drive shafts and or the diff.
On your B series, you do have autolocking hubs but with the benefit that they do not dissengage on changing direction, they stay engaged until you press the 4wd button on the dash.
With regards to your last question, under no circumstances use the 4wd on solid ground, if one of the wheels cannot slip it will cause wind-up in the axles (due to the lack of a centre diff) and could cause catastrophic damage to the diff. (and a front diff on a dti is around £2000

) This can happen in a very short distance, just a few yards. If you are travelling on a road that changes from dry road to snow covered and back again, just press the 4wd button when on snow then pres it agin as you get to dry road again, its so much easier with the Bseries.
Hope that explains it for you