After your marriage, you have to file certain Applications with USCIS (I-130, I-485, I-765, and I-131 if you wish to travel while waiting for your permanent residency). The time frame is rather difficult to predict, but from my experience is anywhere from 5-12 months until you are scheduled for an interview.
Keep in mind that if you are approved, you will be receiving a conditional green card for a period of 2 years and will have to file another petition with USCIS before your green card expires. Also, I do suggest hiring an attorney. It is always a good idea, because immigration laws are rather complicated and before you file anything you should have an experienced attorney review all the factors in your case.
Once you and your fiance have married, you can apply for adjustment of status to that of a lawful permanent resident. Your husband would need to file a petition for you, and you would simultaneously file your application for adjustment of status. If all goes well, the process, including your interview, should be completed within approximately six months.
Using the services of an experienced immigration attorney is a good idea. An experienced attorney will be able to advise you as to what documents you will need, guide you in getting them, and instruct you as to what things you will need to do to get the filing done quickly and with little aggravation. An experienced attorney will also be able to make certain that there are no potential problems, or to be prepared for those which might exist. While many people go through this process themselves, the assistance and guidance of an experienced attorney often proves invaluable.
Good luck to both of you!
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. A consultation with an experienced attorney is always the best way to go.
There are several application forms you will need to complete and provide supporting documents. You will need to go for a medical exam and get fingerprints. You should get your green card in 6-8 months.
If you both will live in Washington, D.C. after getting married, you will be interviewed at the Fairfax, VA USCIS office. Current wait time for an interview at that office is approximately 3-4 months. I agree with my colleagues that working with counsel makes the process much smoother.
Disclaimer: This answer is for informational purposes and does not take the place of a consultation with an experienced immigration attorney. This answer does not create an attorney-client relationship.