nostr:npub1xdtducdnjerex88gkg2qk2atsdlqsyxqaag4h05jmcpyspqt30wscmntxy Trying nsec.app

I've "signed-up" and I have a new identity on my mobile browser. 
Questions: 

1. how can I import my existing keys there? 
2. now if on another browser I do "sign-in" it ask me for public key and.. a password? 

I am confused. In my mind it should hold keys, so I should be able to scan a QR code and store it and that's it. To be clear I expect it to work kind of like Amber but in a browser. 

Am I getting it wrong?