Kerberos tickets work on Linux the same way they work on other operating systems:
Normally, your tickets will be gotten for you during login (i.e., xlogin). If you ever want to get tickets manually, type kinit username, where username is your Athena username. Enter your Athena password when prompted. You can check to see that this was successful by running klist.
Your tickets will last for about ten hours and will become useless after this time. You can use the renew alias to get new tickets. (This command will work on any Athena workstation.)
If you manually get tickets, you should kdestroy them when you are done.