1. to know the meaning of something
2. to know how or why something happens or works
3. to know how someone feels or why they behave in a particular way

Examples

• I don’t understand this math problem.
• Do you understand how the engine works?
• She understands what you’re going through.
• I understand that the meeting has been cancelled.
• The teacher explained it clearly so everyone could understand.
• It’s hard to understand why he made that decision.
• I understand your concern about the project.