Difficult is the opposite of easy. It means that something requires lots of effort to do it. Hard can be the opposite of "soft" (such as a hard pillow and a soft pillow) but it can also mean "difficult."
For example, you can say:
The test was difficult. = The test was hard.
It's difficult to understand the teacher. = It's hard to understand the teacher.
The word hard is a little more informal, so it's better to use difficult in more formal writing.
The word hard can also be an adverb to describe doing an action with great effort or energy. We often use it with the verbs work and try:
Ratan N. Tata has been brought up in an old and well known business family. He belongs to a prominent Parsi family. He has not faced any such financial issues since his family had been successful businessmen since the British rule in India. Ratans father, Naval Tata was adopted by Sir Ratan Tata. He was brought up by his grandmother, Lady Navajbai.Ratan N. Tata is a highly educated businessman. He holds a Bachelors degree in Architecture from the Cornell University, USA, and has pursued and Advanced Management Program from the Harvard Business School, USA. It was in 1962 that he joined his family business; the Tata Group.