After activated TK, you will receive a letter named "Passport photo for TK eHealth card". You have to submit your photo so as to get a insurance card from TK.
Here is an introduction about how to do it: "How do I submit my passport photo for the insurance card?"
It will take 2-4 weeks to receive the insurance card and even longer when semester begins. You don't need to worry because you can always visit hospital with your insurance confirmation.