Vagrantfiles are configuration files for vagrant. The Vagrantfile describes the type of virtual machine, and how to configure and provision the vm.
The primary function of the Vagrantfile is to describe the type of machine required for a project, and how to configure and provision these machines. Vagrantfile are called Vagrantfiles because the actual literal filename for the file is Vagrantfile (casing doesn't matter).
Vagrant is meant to run with one Vagrantfile per project, and the Vagrantfile is supposed to be committed to version control. This allows other developers involved in the project to check out the code, run vagrant up, and be on their way. Vagrantfiles are portable across every platform Vagrant supports.
The syntax of Vagrantfiles is ruby, but knowledge of the ruby programming language is not necessary to make modifications to the Vagrantfile, since it is mostly simple variable assignment. In fact, ruby isn't even the most popular community Vagrant is used within, which should help show you that despite not having Ruby knowledge, people are very successful with Vagrant.
