In its simplest form, Vagrant is a command line utility for managing Virtual Machines. It can create, destroy, manage, etc Virtual Machines in VirtualBox, VMware, AWS and more. The documentation is reasonable and can be found at Vagrant Documentation. We will cover more to the point documentation here.
You will need to download Vagrant from Vagrant Downloads and run the install. You will also need to install the Virtualisation Software of your choice like VirtualBox.
The second command initialises the directory by creating a standard Vagrantfile which will be used to setup the VM. The third will download the VM image from Hashicorp and bring it up.
mkdir /apps/vagrantvagrant init centos/7vagrant up