PS C:\Users\Julien> cd F:
PS F:\> mkdir E:\Virtuals\Ainsible
PS F:\> cd E:\Virtuals\Ainsible
PS E:\Virtuals\Ainsible> dir

The box will be downloaded from the official site: https://app.vagrantup.com/boxes/search

Also, you can check the link for the box from the download configuration file:

Vagrant.configure("2") do |config|
  config.vm.box = "centos/7"  <- Link
  config.vm.box_version = "1804.02"
end

PS E:\Virtuals\Ainsible> vagrant box add centos/7
==> box: Loading metadata for box 'centos/7'
    box: URL: https://vagrantcloud.com/centos/7
This box can work with multiple providers! The providers that it
can work with are listed below. Please review the list and choose
the provider you will be working with.
 
1) hyperv
2) libvirt
3) virtualbox
4) vmware_desktop
 
Enter your choice: 3
==> box: Adding box 'centos/7' (v1804.02) for provider: virtualbox
    box: Downloading: https://vagrantcloud.com/centos/boxes/7/versions/1804.02/providers/virtualbox.box
    box: Download redirected to host: cloud.centos.org
    box: Progress: 100% (Rate: 437k/s, Estimated time remaining: --:--:--)
==> box: Successfully added box 'centos/7' (v1804.02) for 'virtualbox'!

After the box have been downloaded, we are free to initialize it and import it as follows:

PS E:\Virtuals\Ainsible> vagrant  init centos/7
A `Vagrantfile` has been placed in this directory. You are now
ready to `vagrant up` your first virtual environment! Please read
the comments in the Vagrantfile as well as documentation on
`vagrantup.com` for more information on using Vagrant.
E:\Virtuals\Ainsible>vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Importing base box 'centos/7'...
==> default: Matching MAC address for NAT networking...
==> default: Checking if box 'centos/7' is up to date...
==> default: Setting the name of the VM: Ainsible_default_1534168275677_88434
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
==> default: Forwarding ports...
    default: 22 (guest) => 2222 (host) (adapter 1)
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2222
    default: SSH username: vagrant
    default: SSH auth method: private key
    default:
    default: Vagrant insecure key detected. Vagrant will automatically replace
    default: this with a newly generated keypair for better security.
    default:
    default: Inserting generated public key within guest...
    default: Removing insecure key from the guest if it's present...
    default: Key inserted! Disconnecting and reconnecting using new SSH key...
==> default: Machine booted and ready!
==> default: Checking for guest additions in VM...
    default: No guest additions were detected on the base box for this VM! Guest
    default: additions are required for forwarded ports, shared folders, host only
    default: networking, and more. If SSH fails on this machine, please install
    default: the guest additions and repackage the box to continue.
    default:
    default: This is not an error message; everything may continue to work properly,
    default: in which case you may ignore this message.
==> default: Rsyncing folder: /cygdrive/e/Virtuals/Ainsible/ => /vagrant

In order to install the guest plugin, you have to run it from the folder of the box:

E:\Virtuals\Ainsible>vagrant plugin install vagrant-vbguest
Installing the 'vagrant-vbguest' plugin. This can take a few minutes...
Fetching: micromachine-2.0.0.gem (100%)
Fetching: vagrant-vbguest-0.15.2.gem (100%)
Installed the plugin 'vagrant-vbguest (0.15.2)'!
E:\Virtuals\Ainsible>