Not sure why you "can't do" that in Windows 10; file explorer in Windows 10 functions the same way in Windows 8 and 7 in terms of being able to view the files and folders in certain folders by expanding the said folder.
Open File Explorer. Under "View", make sure that the Navigation Pane is enabled. In the Navigation Pane at the left, once you hover your cursor on top of any of the folders listed there, you should see a grey arrow that looks like > - clicking on that arrow would expand the list of folders under whichever folder you clicked that > icon on.