"I have a girlfriend."
Translation:У мене є дівчина.
Both я маю and у мене є mean I have and can be interchangeable but I prefer to use у мене є at the beginning of sentences. Мене means 'me' (accusative) and у мене є literally means at me there is; I'm not sure why it's that way but it just is. Маю is the first person singular of мати (to have). Think of it like "I got" and "I have" in English; we use them both to sometimes mean the same thing depending on context