I am installing a wall oven. There are3 wires in the power box... 2 black and one silver.. which wires do I connect from the wall unit to the power source? Thank you for your help

The question is, does the oven require a 120/240 volt line or just a 240 volt line. Read instructions it will probably tell you. Probably shows a drawing. Post it here.

Silver? Most ovens today need 4 wires-2 black or 1 red and 1 black, a white and a bare copper. Where are you located? If you have a 120/240 you should use 4 although older installs had 3; 2 hots and a Neutral for the 120 side.