Simple Sentences:
* I understand your frustration.
* Do you understand the instructions?
* He understands the importance of teamwork.
Complex Sentences:
* It took me a while to understand the complex mathematical equation.
* Although I understand her point of view, I disagree with her decision.
* The more I learn about history, the better I understand the present.
Phrases with "Understand":
* Make sure you understand.
* I understand what you mean.
* To my understanding...
* I hope you understand.
Variations:
* Understood. (This is a short, informal way to say "I understand".)
* I don't understand.
* I'm trying to understand.
* Could you please explain that so I understand?
The best way to use "understand" depends on the context of your sentence and the meaning you want to convey.