completely reinstall mac mini server

My friend gave me mac mini server saying its Mavericks. When I switch it on I see 2 hard drives only and no operating system. I tried to use my mac ID but it doesn't work. In disk utility I saw 1st hard drive has partition named "os" which I am not able to delete. How do I completely format both the hard drives and re-install Mavericks on that. I have a very slow internet and I don't have another mac, of course I have Linux and Windows dual boot machine.