As Terence Devlin says, you cannot download OS X via anything except a Mac using the the "App Store" application on a Mac OS X 10.6.6 or newer version.
Also you cannot download Mavericks unless your Mac shipped with Mavericks or you previously downloaded Mavericks such that it is in your App Store -> Purchases list.
If your Mac disk previously had Mac OS X Lion or newer OS X version, then there is a change it has a recovery partition.
<OS X: About OS X Recovery - Apple Support>
If the Mac is new enough, it should be able to install OS X via Internet Recovery (a feature in the newer Mac firmware)
<http://osxdaily.com/2014/12/14/reinstall-os-x-mac-internet-recovery/>
If those options are not available, then a friend, or the Genius Bar at an Apple Store.