我给你举个例子1,I can't help (to） clean the room because I am busy.
意思是我不能帮忙打扫房间,因为我很忙.2,I can't help missing my friends when I am lonely.当我孤单时,我会情不自禁想念我的朋友.
总结：can't help (to) do sth 不能帮忙做某事
can't help doing sth 情不自禁做某事