[Spot] Creating bdds

Hi, Can you please explain the api for creating a bdd? How can I create a bdd? How do I define it? How do I give parameter names so that I can later use it to model check a formula? What is the meaning of bdd_ithvar and bdd_nithvar and the int parameter they receive? I would be very happy if you can supply a simple example. Thank you very much and happy new year, Miriam