The worker's cut box while editing or creating a new service is the amount of money that will go to the worker (vs. going to you as the marketplace owner).
For example, if the hustle costs $100 and you have an arrangement with your worker where they receive 75% of each purchase - you would put 75 in that box. You will then receive 25% ($25) as payment while your worker receives $75. This split between you and your worker can be anything.
You can also have different arrangements, with different worker's cuts, for each worker you have on your storefront.