can’t wait to do sth：迫不及待的要做某事

I can’t wait to see how you do all the beautiful things you will do.
我迫不及待的期待看到大家将创造的美好事物。
Can’t you wait until morning to do that? 你就不能等到天亮再玩吗？

can’t help doing sth：情不自禁地做某事，忍不住做某事

I know. I can’t help thinking about her. She is always on my mind.
我知道。我无法不想她，她总在我脑海里。