An acting objective is what your character needs from the other person in the scene. It gives your behaviour direction and turns dialogue into action.
“I want to be happy” is difficult to play because it is private and broad. “I need my sister to forgive me” gives you someone to affect and a result to pursue. The objective should fit the text, matter now, and be specific enough that you can tell whether the other character is helping or resisting you. Once you know it, do not stare at it like homework. Use it. Persuade, threaten, comfort, distract, confess, or bargain as the scene changes. The objective is the spine. Your actions are how you keep trying to get there.
Read the full objective and obstacle lesson