how to create virtual os x mavericks

It's possible using VM software such as Parallels Desktop for Mac or VMWare Fusion.

Why do you need to? You can run your Mac with a second operating system quite easily - partition your hard disk, or use an external hard disk (though this will be slower to run) and install Mavericks on that: however if you haven't used Mavericks in the past you won't be able to do this by any method since the installer is no longer available. Only if you've previously installed it will you be able to download the installer.

Assuming you have a copy of the "Install OS X Mavericks", you use point your virtual machine at the installer and let it do its thing.

If you do not have "Install OS X Mavericks", that is different problem.

You can only run a virtual machine of Mavericks if your Mac is already running Mavericks as the host OS. If your Mac is running any other version of OS X, running a virtual machine of Mavericks is a license violation. You can, however, run Mavericks directly if you install it onto a separate volume and boot up into it.