Translation:I want to know if you are free tomorrow.
For grammar nazis, this is probably better translated are "I want to know if you will be free tomorrow". Generally it's fine to use the present tense in English for something in the future that is certain. In this case it's a question, so it should be future tense. This is for the benefit of any English Literature Professors out there. Strictly speaking the same applies in Italian, but in both languages, widespread colloquial usage is king over any grammar books.