what is this thing on the text frame

I keep instinctively trying to resize my text frames using these......boxes? handles? and clicking on the left OR right one like....sucks my text out and makes a small picture/icon of my text and makes it copy/pasteable. What is this thing even called and how do I make it not do that? I just want to be able to shorten or lengthen text frames without changing their other dimension quickly and easily.
