If you look at the tiny thumbnails in the right sidebar of the Campagins page, you’ll see that there are check boxes next to each of them. The check boxes are used to select campaigns you want to display in your workspace. You can select as many, or as few as you’d like! You can even select campaigns from different groups at the same time.
Another use for these check boxes is to select the ones you want to compare, and then click the Compare button in the top right to compare the stats across those campaigns.