didn't find the add card and save card ID flow

We would like to add Card from the mobile App (developed in Flutter) and save card ID in backend database, from backend we will charge customer from that saved card when needed, so how do we do that?
We have checked this already, checked almost whole document but didn't find the execat flow to add card and save card in backend.

We find remove card api, charge customer api, but didn't find the add card and save card ID flow.