The Visa Bulletin provides updated priority date information for family-based and employment-based green cards. Immigrants to the US are classified into two categories – those requiring placement on a waiting list and those not through their relationship to a US immediate relative. Further, there are numerical quotas on the green cards that require a priority date. If the number of applicants in a year is over the available visa numbers, those applicants are placed on a waiting list and are given a priority date, which estimates when an applicant would get a visa based on the number of previous applicants on the waiting list.
Below is the link for the Visa Bulletin for September 2020: https://travel.state.gov/content/visas/en/law-and-policy/bulletin/2020/visa-bulletin-for-September-2020.html