4 auto

So, this is new to me. Both my JK and jl just had 4 low and 4 hi. Simple, I didn't use 4 hi if I felt good driving over 45 or so. 4 low, I only used off road. Jt has 4 auto. I guess I could just use it all the time, at any speed. (I won't). Also, it seems to shift from 4 auto to 4 high...