VPN, or Virtual Private Network, provides a secure connection between your computer and the resources available at your home institution. Specifically, it permits an authorized user on a verified computer, such as your home PC or laptop, to temporariliy join a secure network, such as SLAC's. In doing so, VPN allows the authorized user to gain visibility of SLAC network resources from outside SLAC.
Such resources include some protected SLAC web sites, or computer systems in SLAC that only accept connections that originate also inside SLAC, such as some database and accelerator systems. For instance, to browse SLAC Oracle web sites from home, or ssh to the accelerator DMZ network while on SLAC Visitor Wireless.
To use VPN, you use your SLAC Windows account, and that account must be specifically enabled for VPN. You can request your account to be enabled for VPN here in ServiceNow.
See the link below for further information on acquiring VPN and its configuration for SLAC. Normally, SLAC managed PCs and laptops come preconfigured for VPN. See the end of the page at that link for how to install VPN on a computer that is not SLAC managed, such as a home PC or personal laptop, and then use it connect your computer to SLAC's network.