If something is difficult, it requires physical effort or brain power to complete, like climbing Mount Everest, a difficult journey.
Difficult has Latin parts: dis meaning "not, un" and facilis meaning "easy." So, something that is difficult is not easy, like marathon running. Difficult can also be used to describe a situation or person that is hard to control. For example, if you babysit a difficult child, he or she might run away from you and not obey you. And you might have a difficult time agreeing to watch that child again.