Use Download menu on the http://www.drillbook.net.
Download and run installation file with the name drillbook.exe. Use tutorial during installation.
DrillBook is usable on computers with Windows 7 and above only.
It doesn't work on MacOS! If you want to use DrillBook on MacOS, you need to install Windows to your Apple computer using BootCamp, or virtual machine via Parallels Desktop, Vmware or VirtualBox.
Read topic How to use DrillBook on MacBook.