please explain: how much ETH for USDC (erc20) transactions?

guys i am total newbie in crypto but have to pay with USDC (erc20), but as i understand i have to got some ETH to make transactions?

how much on average eth , for example, for sending 1000$ in usdc? or swap it to btc in my wallet

The gas fee is not connected to the amount you transfer. You can send 10$ or 10000$ and the fees will be the same. The gas fee is variable based on how many people use the network. Check it out here:
https://etherscan.io/gastracker