There are two ways to create a folder:
In the Campaigns tab, click Create Folder.
Then, search for the campaigns you would like to group together.
For example - Below we are grouping all our PPC campaigns (cross-network)
In the Campaigns tab, check the campaigns you'd like in a folder and click Move to Folder. You will be given the option to create a new folder or add these campaigns to an existing folder.
Want to get organized at the account level? Try making an Account Group.