Read the dictionary definition of understand. All definitions for this word.
1. know and comprehend the nature or meaning of
1. She did not understand her husband
2. I understand what she means
2. perceive (an idea or situation) mentally
1. Now I see!
2. I just can't see your point
3. Does she realize how important this decision is?
4. I don't understand the idea
3. believe to be the case
1. I understand you have no previous experience?
4. make sense of a language
1. She understands French
2. Can you read Greek?
5. be understanding of
1. You don't need to explain--I understand!
See also: Merriam-Webster definition of understand