I am going to have an ultrasound today???

I am taking Clomid, and today is day 15, I am going to have an ultrasound done to see if I have any follicles. Has anyone had this done? What is it like, for example, what is suposed to happen how many follicles, what is suposed to be good? I am hoping I am going to be pregnant, this is my first round of clomid. Any information will be greatly appreciated! Thanks!