To view the critical path of your project, start in the 'Gantt' project layout. You can navigate to Gantt by going to 'Change Project Layout' and choosing 'Gantt Chart'. Once you are there, turn on the critical path feature by going to 'More' > 'Show Critical Path'.
Once this is turned on, you will be able to see the sequence of actions which add up to the longest overall duration and thus determine overall forecasted project completion. This could be a single, unlinked action card or a sequence of cards linked by dependencies as shown below.
To turn this feature off, simply go to 'More' > 'Hide Critical Path'.