I am trying to install a ceiling light to an existing ceiling box. I found two sets of wires, two black and two white in the ceiling box. I believe that this ceiling box is operated by a dimmer switch (just bought house and light was not installed). How do I wire the light?

In most instances like you just described I would say that one set of the black and white wires are the power coming to that fixture, the other set of black and white wires are the switch leg. If this is the case the way to wire the light would be to connect the two black wires together and wire nut and tape. Next connect one of the wires from the light to one white wire and the other wire from the light to the other white wire then wire nut both. Test with the switch before you hang the light.
WARNING: This is not always the reason that you have two sets of black and white wires in a box. You need to check with a continuity checker to find out if two of the wires go to the switch and if the other two are a 120 volt line.

Thank youo. I will try tonight.