As a verb (past participle of "understand"):
* I understood what she was saying. (meaning: I comprehended her words)
* The instructions were clear and easily understood. (meaning: they were easy to comprehend)
* He finally understood the importance of saving money. (meaning: he finally comprehended the significance)
As an adjective:
* The situation is understood to be complex. (meaning: it's generally known to be complex)
* She was an understood friend, always there for me. (meaning: their friendship was unspoken but certain)
* This is an understood rule, even if it's not written down. (meaning: everyone knows this rule, even if it's not stated explicitly)
In common phrases:
* "Understood?" (meaning: Did you comprehend what I said?)
* "I understand, but..." (meaning: I comprehend your point, but I have a different perspective)
* "Understood. I'll get it done." (meaning: I comprehend the task and will complete it)
In formal writing:
* It is understood that this agreement is binding. (meaning: this agreement is legally binding)
* The terms of the contract were mutually understood. (meaning: both parties agreed on the terms)
The specific meaning of "understood" will depend on the context of the sentence.