Understand is a verb that means to perceive the meaning of something, to grasp the idea or concept.
Common usages include:
1. "I understand what you're saying."
2. "She doesn't understand the math problem."
3. "Do you understand the instructions?"
Other meanings:
1. To be sympathetically aware of other people's feelings
2. To interpret or view in a particular way
3. To assume or believe something to be the case