restoring mac and have deleted OS

Hi, I tried to restore my MacBook Pro 2012 to factory as I want to sell it however it looks like I accidentally deleted the OS when I did so. Now when I turn it on it comes up with the question mark folder. I followed some online instructions and started it in internet recovery mode by holding cmd and r. Once this had finished it brings me to the base system page with a few different options, I have been clicking restore OS X and then it takes me to the mountain lion setup thing where I select language and agree t and c’s but then I comes up something like select the drive you wish to install too, and there is no option to click and once I’ve got to this stage you cannot go back and have to restart and it starts the process all again from the question mark folder and requires another hour to get back to this place - PLEASE HELP ME hahaha I really don’t know what to do thanks a lot