A list is a static collection of profiles. Single profiles can be added and removed from any list.
To create a new list begin by going to 'Audience' in the main navigation bar then click 'Lists.' Then click 'New List' in the upper righthand corner.
Next, name your list and select a folder you'd like to add it to or no folder if you don't want to add your new list to a folder.
Once you click save you will be taken to the next screen where you can begin to add profiles to your list.
Search for your profiles in the text bar and then click on the profile to add to your list. You'll notice that when a profile is added it will highlight in blue in the search box and the word 'added' will appear. To remove a profile from the list simply click on the profile again.
When you're finished adding profiles click out of the profile menu. You can always go back and add additional profiles or delete profiles from the list.