When USCIS approves your self-petition, USCIS will tell you of the approval, using Form I-797.
If your petition indicated that you would apply for an immigrant visa abroad, USCIS will tell you of the approval and tell you that the approved petition has been sent to the National Visa Center (NVC). The NVC receives all approved immigrant visa petitions USCIS Service Centers adjudicate.
If your petition indicated that you would apply for adjustment of status and you did not file concurrently, your approval notice will tell you if a visa number is immediately available or the EB-2 preference has a current priority date for filing. Unless you are Chinese or Indian national, then the EB-2 category is probably current for you. If the category is current for you, you can go ahead and file an adjustment of status application (assuming you qualify for adjustment of status).
If you filed concurrently, remember that USCIS will generally consider the adjustment of status application at the same it considers the petition.