You can add Cards to a List from the List or from a search in the Project Library.
Add Cards from within the List:
Expand the toolbar by clicking the
icon, then click the search card icon 
. This opens the sidebar search where you can search for Cards to add to your List.
You can search by typing any keywords, or you can filter the search by Category. Press the filter icon and choose a Category from the dropdown menu.
Add a Card to an empty row
Right-click anywhere on the row and select "Add Existing Card", or "Create New Card". All the other row actions are also available here.
Add Cards to a List from your Project Library:
You can add Cards in bulk to a List from a search in your Project Library.
Click the bookcase icon
on the far left of your screen to access the Project Library.
1. Select the "Cards" tab.
2. Open Advanced Search.
3. Filter your search by Category, Field, or enter a keyword.
Select a Card and the bulk action menu will open.
You can either select the Cards individually, or click 
in the bulk action menu to select all Cards in your current search.
Click the "Add to List" icon 
in the bulk action menu. Select your List from the dropdown menu and click "Save".
The selected Cards are added to your List.