When finding a bill with a star note immediately put it to one side as they are worth more as a collectors item than the bills face value. To determine the value of a star note you found is based upon several things, age of the note, if the bill is creased from being folded, if it was put it in a place where it can lay flat Sosa not to increase the damage, and finally if is either a red or blue star note. Red stars are rarer than blue stars so are worth more. To truly find out the value of your bill go to several local coin dealers and look at what they are charging for the type of bill.
Good luck with your collecting and remember to keep your collection in a safe place and in a flat area so as not to wrinkle the notes that will decrease the value of your find.