Parallels Tools is a set of tools developed by the Parallels company shipped together with their Parallels Desktop virtualization software. The tools provides improved integration of a guest system and OSX.
The main part of installation is the same as for any other Linux distribution; you can just follow the official instruction from Parallels until the last step.
When asked if you want to reboot the virtual machine, choose No. Otherwise the boot will fail.
Before rebooting your machine, it is necessary to remove prl-x11 from autostart, since it can lead to OS boot stall.
cd /etc/
find . -name "???prl-x11" -exec rm -f {} \;
reboot