Congratulations! I was 18 when I got pregnant, and I was very scared. But trust me, everything is working out. First of all, go to a health clinic. They will most likely do a free pregnancy test and basic exam and determine your due date...and you can sign up for medicaid! Don't be ashamed to take assistance in the case of your baby's medical care. Your mom and dad work and pay taxes just like everybody else, and so do I, and I'd much rather my tax money went to keep your baby healthy than went to buy recreation materials for prisoners.
Then talk to your partner. Make a plan. Are you finished with school? Are you working? If you're planning on moving in together, figure out who will pay what bills and what will happen after the baby is born. Will you go back to work, stay home with the baby, or go back to school? Will you put baby in daycare or do you have an aunt or friend who already stays home who could help out?
Once you have a plan, talk to your parents if you haven't already. I say AFTER you make a basic plan because they WILL be angry, but they will take you much more seriously if you have a plan for work and school and daycare already, than if you just go to them and say, "I dunno." They will be mad, but trust me they will love that grandbaby and want to take care of him or her. Just don't dump the baby on them to raise...that's trashy and you're better than that!
Start saving your money. Even if you buy some things secondhand, plan on spending AT LEAST $1000 in baby things for baby's first year. Don't freak out! You can do it! If you and your partner both work 25 hours a week for $6/hr, you can easily have twice this much by the time baby comes. You'll need a crib, dresser, carseat, stroller, diapers, wipes, and toiletries...not to mention clothes and toys. You can start looking for bargains and sales on these things now, and don't be ashamed to buy from yardsales or borrow from friends and family! Also you'll get a shower and people will give you some nice things.
You can do this! Please stay in school if you haven't finished. It's best for you and baby. And even if you and the father aren't together, he IS financially obligated to help you with his child. Buy the book What to Expect When You're Expecting and Your Pregnancy Week by Week...it will really explain your baby's growth and what your body is going through, and what you need to do and not do, etc. Good luck!