Having a document open in a different window allows you to view both documents side-by-side. To move a document to a new window, drag-and-drop the tab outside the window. Select New Group to create the group.
Selecting Drop Here is equivalent to drag-and-dropping a file from File Explorer.
To move the tab back to its original window, drag-and-drop the tab to the original window.
A secondary method to create a new group are the Window | New Horizontal Group/New Vertical Group commands.
While creating a new group displays two different files in different windows, you can split a window to view documents in the same window.