First (EB1): Priority Workers
Second (EB2): Members of the Professions Holding Advanced Degrees or Persons of Exceptional Ability
Third (EB3): Skilled Workers, Professionals, and Other Workers.
Fourth (EB4) : Special Immigrants/Religious Workers
Fifth (EB5): Investment/Employment Creation
What is a Priority Date?
Green card process start date is the Priority date. For employment-based applicants, it is the date on which labor certification was received or the date that the USCIS received the Form I-140 if the labor certification was waived.
How do I know my official priority dates ?
The I-140 approval notice will have offical the priority date.
Where does the priority date help ?
Priority date has to be current, for you to apply for I 485 or adjustment of status. Basically, priority date decides when you will get your green card and how far ahead or behind you are in the green card queue.
How do you I know the current priority date ?
what is being processed or to be processed is given in Visa Bulletin.
What is EAD ?
EAD is Employment Authorization Document. It has to be applied seperately after applying for I 485 on employment based green card. EAD allows you to work for the validity of the card -- it may be 1 year or 2 years depending on your status.
What is Advance Parole ?
Similar to EAD, this also should be applied seperately after applying for I 485. This is like visa that can be used to enter US on pending green card applications. Certain restrictions apply, you can use it only for emergency purposes.
Disclaimer: I am not a lawyer. Its always better to do the green card process through an immigration lawyer and consult specifically on your case.