Did you have a specific question? Because what you're asking is in general answered in the lesson. Can you give an example where you experience difficulties?

-- Chris. 

I understand that we use quel(s) quelle(s) when there is a choice, to mean "which person/thing", but in case of 'quelle est votre addresse?' here there is no choice, this is more of a definition, and it doen't sound like an adjective as well.. so why "quelle" and not "quoi"

Have a look at this site:

https://french.stackexchange.com/questions/5933/when-to-use-quel-or-quoi

-- Chris.