The only silly question is the one not asked. I guarantee you there are a lot of people on this site that don't know what scratch is. We all learn things off here.
Nwgirl is correct in treating it like chicken candy. Scratch is high in energy and too much is dangerous for a chicken, just like too much candy is dangerous for us humans. If they eat too much scratch, they can build up fat in an internal organ, the liver I think, and it can kill them. It doesn't happen every time but it does happen. The rule of thumb is to give them only what they can clean up in 10 to 20 minutes. Your goal is a balanced diet.
Since it is high in energy, some people like to give scratch just before the chickens go to bed on cold nights. The thinking is that the scratch helps keep them warm at night. Another good use of scratch is to throw it on their litter. They will scratch through the litter looking for the scratch and stir it up so you don't have to. I wonder why it is called scratch?