Calculation of the critical path is a little more automated in Project 2010. All tasks, after all, are on the path to project completion. Project therefore decides based on your task duration and task slack whether or not a task is critical. Once you have listed your tasks and estimated durations or dates, you can then ask Project to identify those tasks deemed critical. Initially in the project represented in the view below, only the ending task was identified as critical. However, asking Project to calculate multiple critical paths shows us several tasks that require some focus.
There are two ways to ask Project 2010 to show you the critical path. FIrst, you can go to the Format tab (it's a contextual tab, meaning it appears only when it's relevant), look in the Bar Styles group, and find the checkbox for Critical Tasks. Selecting this will highlight the minimal tasks that Project deems must be accomplished to finish the projecct. You can also go to the View tab, in the Data group, and click on the Filter icon. In the drop-down box, choose Critical. Again, your critical path will be highlighted.
Sometimes Project identifies only the final task as critical. In order to manage your options, go to the backstage view and click on Options, then choose Advanced. Scroll down to the section at the bottom section called Calculation Options for This Project. Select the box for Calculate Multiple Critical Paths. You can also adjust slack time in this section.