P.M.
It all depends on the state you were adopted from. Many states have opened up their previously sealed records and all you need to do is contact their Vital Records department and request your original birth certificate. Sadly, if you are like me and surrendered in Florida, it's a long journey to your answer. Here is a list of open record states: http://www.omnitrace.com/states-open-adoption-records/
Adoption.com is a WONDERFUL resource for getting started. They have a huge area of information and support for adult adoptees. The searching process is an emotional journey and it helps so much to be involved with those going through the same things. They have many FAQs about starting your search. You can find them here: http://adoptees.adoption.com/
Of course you can contact your adopting agency or law firm (remember that you must be at least 18 years old to do any of this) and see what their record policy is. If your state is open records, they will more than likely just send you all your information. If not, you're back to square one unless you want to petition the court for your records. Most courts in closed-record states will deny your request unless for medical reasons, in which case you are only given medical information; not contact. Do not stop at your adopting agency if they prove to be a road-block, there are many more options for you.
Good luck on your journey, I hope the road is easy.