SSL/TLS VPNs use the same encryption that protects HTTPS websites. They run on TCP port , so they work through almost any firewall.
Clientless SSL VPNs provide browser-based access to web applications. You log into a portal and access internal sites through the VPN gateway's proxy.
Full tunnel SSL VPNs require a client application. They create a virtual network interface and route traffic through the encrypted tunnel. OpenVPN and Cisco AnyConnect use this approach.