Im thin but sooooo out of shape b/c i just quit smoking... help!?

I'm a 26 year old female. I'm 5"5 and 125 lbs, but I have the tiniest bone structure in the world... my ring finger is a size 4, and my ankles are the same size as my skinny 7 year old niece's For my body type, I should weigh 115 my doc said. I was laid off a year and a half ago, and the only time I get off the couch is for an interview or to smoke a cig. I quit smoking and want to eat right and exercise to be healthy and lose 10 pounds... any tips?