Watch the Video
Read the Doc
Anytime you select a contact or account, buttons will appear at the top of the UI that allow you to take action on them. If you select the 'List' button, you'll be able to add them to lists -
From the modal that appears you'll be able to select lists that already exist or create a brand new one to add them to (shown below) -
Note: Anywhere you are able to add people/companies to lists you can create a list from the same modal.
Go to the People page and click the List tab at the top of the page -
This will bring you to a page containing all your lists for you to filter and search through, as well as create, edit, and delete Lists -
Note, however, that you do not have to be in the People/Companies pages to add or create lists. These are just the common starting points. When a contact/account has been selected in a list, you can generally add/remove lists by using the buttons that appear at the top of the UI. When viewing a contact/account profile, however, you can add lists by clicking the Edit button to the right of the 'Lists' field, shown at the far right of the profile.
Removing Contacts and Accounts from Lists
If you need to remove contacts or accounts from list you can select them in the same way you would when adding them, and then choose "Remove from Lists" (the process is the same for accounts, but you do this on the Companies page instead):