Padding is the empty space inside a box, between its contents and its edge. It is like the soft lining inside a parcel that keeps the item from pressing against the cardboard.
A button needs padding so its words do not sit right against its border. Adding more padding makes the button roomier without pushing other page elements away by itself.
Padding is different from margin, which creates space outside the box. If text feels cramped inside a card, adjust padding; if two cards are too close to each other, adjust their outside spacing.