IPSec can be used to create a secure session between a client computer and a server. For example, you may have the financial data on a financial server. All members of the finance team will have IPSec tunnels created between their desktops and the financial server. This will prevent anyone using a packet sniffer stealing data from the financial server or any session across the network.
IPSec can also be used as a VPN protocol as part of the L2TP/IPSec tunneling protocol that is used by major vendors who create VPN solutions, such as CISCO, Microsoft, Sonic Wall, or Checkpoint.