what is the start date of the extension visa? biometric date

or decision date?
I will be happy if you you can explain to me what is the biometric, I gave my biometric data in the initial application, do I need to give it again in the extension? and what is the biometric card? who need it?

the second and the main question is: I need that after applying for the visa, the decide and if they accept it, then they invite to give biometric data,.
when is the start date of the visa, the date of the decision or the date of biometric appointment?

Please continue in your previous topic.