question about selections for Olympics and other Intl events

As an only 3 year fan, the more I learn, the more questions I have.

So using USA figure skating as the example. how do they decide who goes where? For A teams Olympics and B teams 4 continents.

1. how do they account for scoring..eg if a skater has a high score from a Lombardia Tophy or Warsaw cup, but the rest of the score are much lower. is this looked at?

2. same question for points but placement also can reflect if the competition was not strong.

3 how important is the nationals performance.

appreciate any thoughts. am particularly am interested for ice dance.

thanks in advance