Q: Installing OSX 10.11

I cannot tell since the underside is a tad scratched up..

I am trying to install where it says Reinstall OSX on the OSX utilities.

Another thing is I cannot find any startup disks on the menu either Isn't there a way to reinstall the OS that came with it before I got it? But like I said there is no back up..

Sorry but I am unable to make it any clearer

Apple menu. Startup disk... Restart, shutdown.

If I click the tab next to it and then try to leave utilities it says to choose a startup disk but the menu to select said disk from is empty..

I had a feeling it was my HDD... I cannot erase the Macintosh HD and as for the "base system drive??" it does not give me the option to erase..

I cannot, I suppose this is the end and that I need a new HDD