Ok, i have a parakeet and she laid and egg that i found while cleaning out their cage and I freaked out?

alright, so i was cleaning bluebells and Gracie's cage and i found a little white egg under their food dropping place (where they drop the shells of the seeds ETC.) i freaked out because i thought both of them were girls. i got them about a year and a half ago. no other eggs have been found so far (the one i found had a hard spot in the middle of a soft spot and it was infertile) and i don't know anything about raising baby parakeets and nesting boxes or any of that stuff. i can get my grandpa to make the nesting box and get all the materials but i still need some info on how to raise them if something goes wrong (like if they reject the babies or not) thanx :D