I "assume" you purchased this used and did not get an instruction sheet?
The sheet tells you where the 3 wires connect, and also how to use the unit.
Installing it is simple, only 3 wires to connect.
Ground wire can be fastened to a screw that hold the ALDL connector to the underside of the dash.
Power wire can go to the fuse block in a switched source.
Data wire can be spliced into the orange wire in the ALDL.
If this is confusing you, go do LOT of research, or sell the car!
Actually, you do need an instruction sheet to read the unit, and I can mail you a copy if needed.