can drywall be apply over plaster
Yes, you can install drywall directly over plastered walls. First you need to solve the  water intrusion issue that damaged your plaster, or the drywall will end up being damaged the same way the plaster was.

Installing drywall over plaster is the same as installing it anywhere else except you may need longer fasteners (nails/screws). This forum is not the place to give comprehensive instruction on drywall installation but there are many sources for you to get that info...