NetScaler Gateway Express License: The Express license is used with the NetScaler VPX and allows for up to five concurrent user connections by using Receiver or the NetScaler Gateway Plug-in. The Express license is available for the VPX appliance and expires after one year. Users can connect to either Basic or SmartAccess virtual servers.

NetScaler Gateway Platform License (ICA license): The Platform license allows unlimited user connections to published applications on XenApp or virtual desktops from XenDesktop. Connections using Citrix Receiver do not use a NetScaler Gateway Universal license. These connections only need the Platform license. The Platform license is delivered electronically with all new NetScaler Gateway orders, whether physical or virtual. If you already own an appliance covered by a warranty or maintenance agreement, you can obtain the Platform license from the Citrix web site.

NetScaler Gateway Universal License (CCU license): This license allows VPN connections to the network from the NetScaler Gateway Plug-in, a SmartAccess logon point, or Secure Hub, Secure Web, or Secure Mail.

Use Serial Number. The software internally fetches the serial number of your appliance and uses this number to display your license(s).
Use License Activation Code. Citrix emails the LAC for the license that you purchased.

Sample commands:

login: nsroot
Password: nsroot
> shell
root@ns# mkdir /nsconfig/license
root@ns# cd /nsconfig/license

Copy the new license file(s) to this directory.

sh ns license
show feature
enable feature lb