I got that letter as well from NVC and I was able to login with my credentials provided. Your priority date on your application will determine when more steps are allowed to go forward on your case. It is a very very frustrating wait time given the number of years it takes for them to process the visa given the framework set out by the INA. Just being patient is our best attribute to get through this whole process. I have found tons of information here that helps beginners like myself but it would be really good if someone could create a calculator that shows when one's priority date will become current (maybe out there already, idk).