The screenshots below show the different places where Custom Action buttons can be displayed.
Display Form Buttons
Custom Action buttons can be shown in the ribbon of an item that is opened in Display mode.
Edit Control Block
Custom Action links can be shown in the "Edit Control Block", which is the menu that appears when the three dots next to an item is clicked in the list view.
List Ribbon Buttons (Items tab)
Custom Action buttons can be shown in the List ribbon (Items tab) when in a list view.
