Dear Sarina,
one of the few thing in common between qlikview and qliksense is the backend, so the script; also theformulas and set analysis are the same,. The rest is something new so you need to spend some hours to understand how it works. Generally Qlik Sense layout is easier than qlikview, also the possibilities/customization are less.
I have no knowledge about power bi so i cannot help you to compare it.
I suggest you to but some good guides like "mastering qliksense" or "learning Qliksense" to have a good base where to start using Sense.
Michele De Nardi
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