What is the utility of the small port above the usb 3.0 port in surface 2?

[Windows Central Question]

Hi! I am now an owner of a surface 2 10.6 inch 32 gb tablet. I want to know how I can use the small port on top of the 3.0 USB port in my tablet. Also please let me know how to deal with this device when it slows down. I have a HP 540 laptop of 7 years at home and as I am not update in the computer know how, I don't know how to clear the temporary files which I do with "prfetch" & "%temp%" orders in my laptop that comes through the "run" order in startup menu.