images through a few specific methods, though you must be careful to avoid unauthorized or "distro" versions that may be unsafe. Recommended Download Methods
OS X Mavericks 10.9: Official Download and Installation Guide
For supported Macs, you can boot into (Command + Option + R) – but this installs the original OS that came with your Mac. For a 2009 MacBook, that may be Snow Leopard, not Mavericks.