The Office Web Applications (Word, Excel and PowerPoint) are now fully integrated with Teams.
With this integration you can create new documents directly from Teams as well as open recent files (using the same UI than the full client).
To do so, just open the ellipsis (the …) option to search for any of the Office Web Applications
Then when selecting the application you will be in the Home of the application to either create a new document or open a recent one
If you right click on the application in Teams you will also have the option to pop out the application to split your Teams window and Office window