The critical path is the longest sequence of tasks that determines the project duration. This feature highlights all the tasks on the critical path with the red colour. Tasks on the Critical path will also be listed in the Gantt Infobar.

To highlight the entire sequence, you must define dependency links between tasks. Only the strong links that impact scheduling will determine the tasks on the critical path.

Once you establish task dependencies, the App will automatically draw the Critical path. To display it, click on View > Critical Path. 
You will see your Critical Path tasks highlighted on the timeline and listed in the Infobar. For example, task BPV-22 is linked to BPV-21 using the 'End to Start' strong link. Since changing the duration of these tasks will impact the entire project, both of them are on the critical path together with their parent tasksBPV-20.

Dependency lag time and ASAP mode

Some activities will depend on the completion of others. Use strong links to determine the correct order. When creating a dependency you can set the lag time or the ASAP which both condition whether the task is on the Critical path or not. 

For example, if a gap between linked tasks (End to Start) is greater than the defined lag time, the preceding task will not be on the Critical path.  If the gap between linked tasks (End to Start) is one or more days and the ASAP mode is disabled, the preceding task will not be on the Critical path:

Non-working days

The non-working days are have no effect on the critical path calculation. This means that if there are two tasks with a dependency on the critical path and the predecessor ends before a non-working day, the App will move the successor to start on a first working day and both will remain on the critical path: