Joint compound is sometimes referred to as drywall mud. It is used to cover seams between pieces of drywall or sheetrock and to patch holes.
Only fresh joint compound or mud should be used in any project. Fresh mud is easier to spread and generally works better. If you notice some of the mud has dried, discard it.
Most joint compounds come in either one-gallon or five-gallon buckets. You will need to determine how much compound is needed based on the size of the project. Deep joints and heavy finishing require more joint compound. The easiest way to mix joint compound or mud is to use a mixing paddle. This is a bit that attaches to a drill, almost like a blender extension. Attach the paddle bit to the drill. Slowly begin mixing the joint compound. You are looking for a creamy-like consistency and do not want any thick pieces in the mud.
Cleaning up drywall joint compound involves water and elbow grease. Clean tools, hands, etc. Dried compound may require additional rubbing for removal. Use caution when cleaning taping knives to avoid injury.