A few weeks after your application has been received by USCIS, they will send you I-797C, Notice of Action, Receipt Notice.
Using the receipt number in it, you can track the process of the case online.

Depending upon the category, it may take a few months or even few years before the petition is processed.

If USCIS needs any additional information, it will mail you a letter called RFE (Request for Further Evidence) asking for it. Follow the directions exactly, and make a copy of everything you send.

Once it is processed, it will either be approved or denied. USCIS will notify the petitioner if the visa petition is approved, and will send form I797, Notice of Action - Approval Notice.

An approved petition is only used to demonstrate a qualifying relationship. An approved petition DOES NOT grant any benefit, it simply creates a place in line for visa processing.

USCIS will then send the approved visa petition to the Department of State's National Visa Center (NVC), where it will remain until an immigrant visa number is available.