On July xx, 2018, we began reviewing your Form I-130, Petition for Alien Relative, Receipt Number MSCxxxxxxxxxx We mailed you a notice informing you of the action we intend to take on your case. Please follow the instructions in the notice and submit any requested materials.

I need a help and so far i haven't got any mail from USCIS. what does it mean?
Do i have to worried or its a normal case?
Highly appreciate with your comments.
Thanks you.