Formatting hard drive question
I've got an early 2011 MacBook Pro that is currently running OS X El Capitan. About a year ago, my hard drive failed and I replaced it with a Samsung SSD. I've had no problems at all but I'm wanting to format this drive before I upgrade to Sierra as there's loads of stuff on here that I want rid of! I'm just a bit confused about what to do though. When going into Disk Utility after restarting my Mac, in the right hand column where you select the drive, I get the SSD, but there is also one called OS X Base System? What is this? Can I get rid of it? Also, if I do format the SSD, how do I go about getting OS X back onto it. When I first put it in, there was some sort of internet recovery thing I think, will it just be the same procedure?
Thanks!
MacBook Pro (15-inch Early 2011), OS X Yosemite (10.10.3)