said, on the 757 only some of the spoiler panels are used for both roll control and speedbrake in the air. On the ground, all panels raise with speedbrakes deployed.
The 767 is an exception, all
the spoiler panels are used for roll control and speedbrake, both in the air and on the ground (if memory serves...).
"So when I saw the outboard spoilers engaged at the beginning of our descent,was that an autopilot input or something the pilot would engage to assist the autopilot?"
That would be a pilot input to increase the rate of descent to get the aircraft back on the idle descent path. Once back on the appropriate descent path the speedbrakes can be re-stowed for a normal descent. This is common practice when we are given a slightly late descent from ATC (so the aircraft passes the FMC-computed T/D point before a descent clearance is issued).
It can also be required with descent in tailwind conditions where the high ground speed will result in the angle of descent less than the idle descent path. Like Cx_flyboy said, the "DRAG REQUIRED" FMC message is the one to watch for here.
I used to love the smell of Jet-A in the morning...