"I am number one, do you understand?"
Here's a breakdown:
* Yo soy: I am
* numero uno: number one
* a: a (this is often omitted in informal Spanish)
* you: you
* comprendes: understand(s)
The phrase is a boastful statement, implying that the speaker is the best or most important. The phrase is often used to express arrogance or a lack of humility.