Thanks for giving it a shot and sorry for the trouble. I left it vague with the hope of people would figure it out, but I think it's way too vague and I didn't get to improve it in time. Anyway, after clicking the red thing to pick it up, you can place it on any of the dark brown spots (the lining of the blood vessel), and that's when the game starts. You can also move them after placing them, and buy more once you earn more peptides (the unnamed currency, fwiw).