For a K1 there is nothing to upload. You fill out the DS160 form on the site I linked above before you can schedule an interview.
You bring the required documents along with the i-134 from the US citizen for financial support with you to the interview, where they will look at them during/after the interview.
The fees must be paid in person at an EcoBank branch, along with a print-out of the receipt that you'll get from the interview-scheduling site. There is at least one money transfer app (Xoom) which allows pick-up at EcoBank, if you're not comfortable carrying that much cash around.
Also, it helps others on the site give you advice if you fill out your timeline. That also helps others know when they might expect their own approval to come.
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