How the Vinted fee works
Vinted adds its fee at checkout, on top of your price. Vinted's Australian price list says it's usually 5% of the price plus $1.20 per order, and that the exact amount depends on the item, the order value and whether it's a single item or a bundle. Vinted calls it the Vinted fee; the address of its help page still says "Buyer Protection fee". Nothing comes out of your money, but buyers see the total, so it's worth keeping in mind when you price.
Who pays postage
The buyer. Vinted says "buyers cover the shipping costs", and the price shows at checkout. In Australia, parcels go with Australia Post: you print a prepaid label or show a digital barcode at a Post Office, or use a printed label at an Australia Post Parcel Locker. You have 5 business days to send the item. See the postage guide for what Australia Post charges.
When you get paid
Vinted says you're paid "as soon as the buyer confirms everything's OK". Buyers have two days to report a problem after Vinted tells them the parcel has been delivered.
Costs the calculator leaves out
Vinted sells optional Bumps to make a listing more visible. The price depends on the item's price and whether you bump for 3 or 7 days. It's your choice, so it isn't included here.
Selling as a business
Selling your own unwanted clothes is generally not taxable. If you buy things to resell for profit, that can be a business. See tax on selling online in Australia.