You can use the Actions menu from the Constituents grid. Go to Workspace>CRM>Constituents.  Select Actions, then select Create Email List.

A new window will open to allow you to add the constituents to an existing list or create a new list. With Create New List selected as NO, you will select from a list of your existing email lists. Once you select the list, click on Save to add everyone showing on the grid who has a primary email address to that email list. If they are already on the list, it will not add them again.

Selecting YES for Create New List will allow you to enter a name for the List Name and select a List Category that this new email list will be associated with. List Category can be considered an area of interest. You can learn more about List Categories here: https://support.donorview.com/en/support/solutions/articles/9000030516-can-i-categorize-my-email-lists- Click Save to add your new email list to all the constituents with email addresses showing on the grid.