Gmail's most recent overhaul came with lots of changes, and some people don't like its new toolbar buttons, which have icons instead of the arguably more descriptive text. If you want the old text buttons back, you now have the option to switch them in Gmail's settings.
To toggle the buttons back to text, head to Gmail's settings. Under the General tab, scroll down to "Button Labels". click on the radio button next to "Text", save your changes, and head back to the inbox to see the new (old) buttons. Of course, if you like the icons but just wish it were a bit easier to differentiate between the buttons, there are other ways to do that too.