How to download VM back-end servers ?

Sarah, that's a pretty vague question. It sounds like you need help setting a lab using VMware Workstation, to include a web server and other tools. I suggest you start with the VMware documentation for standing up virtual machines. For a web server, it may be easiest to deploy something like a Turnkey Linux VM. As for F5 products, those are located on the download page from the support site.