I have a question about Kela and I hope you can help me!

In August I'll come to Helsinki to be an Au-Pair for at least a year. I'll get a residence permit for I think at least a year.
My question is if I'll be able to get a Kela card? I've been on the Kela homepage but I didn't understand all the info..
Well, I'm also not really sure if I understand what Kela is.
On one hand it is the health insurance card but on the other hand it is (at the same time?) an identity card that you need in your everyday life in Finland? For example to open a bank account or to get a library pass?
I also read about an identity card from the police. Is that the same?
Sorry, but right now I'm really confused..

Thanx in advance and best wishes, Kristina