VASP is copyright protected, this means that if you are not a member of a research group that has the license, you must buy one to use the software. More details are shown in their website: https://www.vasp.at/info/faq/
After having a license, you could see the installation process at their wiki, https://www.vasp.at/wiki/index.php/The_VASP_Manual, it's pretty simple.