"My sister has told me what has happened in the hospital."
Translation:Meine Schwester hat mir erzählt, was im Krankenhaus passiert ist.
This is a dependent clause and verb goes at the end. This distinction haben/sein is not clear to me.
Motion verbs use sein, while non-motion verbs use haben. That's about 90% accurate and extremely simple to remember.
Ich bin gegangen. (bin + motion verb (go))
Ich habe erzählt. (habe + non-motion verb)
Yes, but I did not think "passieren" is a "motion" verb !! Is this an exception ? Thx !