Welcome to Berlin! If you want to stay here you have to register yourself and your sister and to apply for asylum. As a first step you have to go to the institution for the first admittment, in Berlin it's called LAGeSo.
LAGeSo is located in Turmstraße 21, House A in 10559 Berlin Moabit. Cause every refugee and asylum-seeker in Berlin has to go there, the waiting time is very high. But there are some social workers and volunteers who take care of you.
You reach LAGeSo by bus number 101, 123, 187, 245, the airport bus TXL or the subway (U-Bahn) U9 Turmstraße.
I wish you all the best here in Berlin! Good luck :-)