1、做定语：a difficult task一次很难的任务。

2、作表语：this task is difficult.这次任务很难。普通形容词都可以如上用。

3、句型：it is difficult for sb to do sth:做某事对某人来说很难.如：it is difficult for me to do the task。

4、名词是difficulty句型：have difficulty (in) doing sth。