Critical Path Method includes determining the longest path in a network diagram and the earliest and latest an activity can start and the earliest and the latest that activity can be completed.  Here are a few basic things you need to think about.

• It is the longest duration path through a network diagram and determines the shortest time to complete the project
• It helps prove how long the project will take
• It helps the project manager determine where best to focus his or her efforts
• It provides a method to compress the schedule during the project planning phase and whenever there are changes
• It provides a method to determine which activities have float and can be delayed without delaying the overall project.

The easiest way to find the critical path is to identify all paths through the network and add the activity durations along each path.  The path with the longest duration is the critical path.