Vagrant is a tool to create and control Virtual Machine environments simply. It does not run the virtual machine -- that is done by a VM provider such as VirtualBox, Hyper-V, VMware, or Docker. Vagrant does the fiddly work of connecting network interfaces, shared virtual disks, and provisioning scripts. Your configuration details are specified in a Ruby language file, always named "Vagrantfile".
There might be several Vagrantfile instances an a project, and more than one
may be consulted in building a virtual machine. We will concern ourselves with
only one. It will be in our directory, or a parent of it. It will define two
essential things: the name of our machine, and where to find its bootable image.
Vagrant bootable images are packaged in a "box".
Vagrant boxes may be created
by your company (or yourself, but they are not trivial to make) or downloaded from
a public repository. Each box may be
built for one or more of the possible VM providers.
Lessons here will use either VirtualBox (the default) or VMware to run the VMs. If you wish to use VMware, you will need to buy a commercial VMware provider for your workstation. If you use only VirtualBox VMs there is nothing to buy.