hard可以做形容词使用，表示难的，硬的

hard也可以做副词使用，表示努力地，辛苦地等

For example:

This question is too hard for me to answer.难的

The bed is so hard for me to sleep well.硬的

It rained hard so that I couldn't go out for a walk.

I will work hard to make my dream come true.