Consider an agent trying to maximize its Pacman score. 'Getting a high Pacman score' is a terminal goal for this agent - it doesn't want a high score because that would make it easier for it to get something else, it simply wants a high score. On the other hand, 'eating fruit' is an instrumental goal for this agent - it only wants to eat fruit because that increases its expected score, and if eating fruit didn't increase its expected score then it wouldn't care about eating fruit.

That is the only difference between the two types of goals. Knowing that one of an agent's goals is instrumental and another terminal doesn't tell you which goal the agent values more.