virtualbox.org

I'm taking an Alison course on ethical hacking, and they told me to install VirtualBox and a bunch of iso files. I set up the windows 2012 server and then moved to the windows 10 client to join the domain I created before.
however, in the video you click "use domain login instead" or something, but that didn't appear for me. not only that, I followed the instructions to change my windows 10 client DNS to the same one I used in the DNS from windows server 2012, as well as a specific ip address. then, they told me to ping the server to make sure i was connected. despite following all instructions i could perfectly, it still says destination host unreachable. can someone help?
some additional information: the kali linux machine, the metasploitable machine, the windows server 2012 machine and the windows 10 machine are all connected to host-only adapter, like they asked in the course. do I need to reinstall windows 10 again? i already did this 5 times before

Joining a client computer to a domain isn't part of the scope of this forum, but we can certainly help checking that the virtual environment is set up correctly for a domain lab.

A lab for a Windows domain should be done with the VMs connected to one "Internal" network. Internet can enter the lab through the server VM, if you want to set up a second network adapter in the server VM and enable router services in the server OS (I think that this is not recommended to be done on a domain controller). Or you can set up a router OS VM to inject internet into the Internal network, and have the domain controller handle the DNS etc. See Virtualbox Networks: In Pictures: "Sandbox"

The Sandbox setup most closely simulates a real-world office domain:
The DC and clients will all be peers on the Internal network, then the clients can connect to the domain. If you add a router VM a la Sandbox, the router OS does not have to be (and shouldn't, if I understand properly) try to attach to the domain; it would only be a non-domain peer on the Internal network, behaving just like a router on the real office domain.