Just a quick question: my HDD died and I will buy an SSD. However, how can I boot the Mac with a blank SSD? Do I have to buy an external box to connect it first to a computer and download something?
You can use Internet Recovery to pull down a OS X installer - if I remember correctly, it will install the original OS that came with your computer, and then you can grab the latest installer: https://support.apple.com/en-us/HT201314