lumina trans for dummy

Just bought 1992 Chevy lumina...
And wandering what (D) and D means, what's the difference?
First D comes circled, and second just standing along.
Can anyone help me with that?
thanx.

[Overdrive] and Drive.

4th gear for better economy when cruising.

D in circle is overdrive?
Is it ok ti use this one constantly, or it has no effect until highway?

Yeah, just leave it in OD. About the only time you'd ever wanna put it in D is if you were driving on a rolling road at speeds near OD threshold, and it kept shifting in/out of OD and was getting annoying. This doesn't happen much. But on rare occaisions you might find that happening.

You can use it for a little additional speed control in certain instances too. A place near here is a known speed trap, and the road is gentle rolling hills with a 50 mph limit. In OD, it'll roll upwards of 60 mph on the down hill pretty easy, so a lot of the time I'll just put it in "D" and set the cruise at 50, and it won't pick up speed quite so fast downhill, so I don't have to watch the speedo so close.

About the only other time I use "D" is if I go flying by a state trooper well in excess of the limit, I'll drop 'er down to "D" to knock off some speed without hitting the brake. ;)

P.S. to answer your other question, OD will engage at any speed over 35 or so when there is no real load on the driveline (cruising). It'll downshift outta OD as demand warrants.

Thanx for your replies! =)