Hey,
As a K1 applicant, I know that the embassy will contact you with instructions on how to proceed (it's a pretty straight forward email telling you to schedule your medical and your interview). You can also go ahead and email them to let them know you're waiting for their instructions, they'll usually respond within 3-5 days. What I would advise you to do is go ahead and fill out the DS160 Form and create your account on the Embassy website in order to get a shot at an appointment slot in good time. You will have to wait for slot to open in order to pay for the interview, (wait a couple of days until your payment is confirmed), then wait again for other slots to be opened (because obviously in the time you're waiting for the payment confirmation, the slots that were initially available will have been taken) to schedule the actual interview.
I hope this helps.