Directions on the fecal test for dogs?

Okay so I have a 5 month old puppy and we took her to the vet today they said we needed to give her a fecal test. They gave us a box with a plastic bag inside and a small bottle which was inside bag. The bottle says,"Labsco 10% formalin fixative neutral, phosphate buffered." Have no idea what that means though haha. About half the cup is filled with a liquid substance.The problem is they didn't really tell us how we do the test. All the lady said was "just put the dog's poop in the bag and send it to the places address that's on the box." Simple right, The only thing is the bottle totally threw me off and I have no idea what I should do with it. Please help, thank you!