When you create an NFT, you have the opportunity to decide on the percentage of royalties you would like to receive from future sales.
For full instructions on how to create an NFT, visit: How to create an NFT
In the Create New dialogue box, you can choose anywhere from None to 30%:
Make sure you consider the percentage carefully. Once your NFT is created, you won't be able to change your royalties.
In the future, every time your NFT is resold, you will receive the percentage of royalties that you chose at the time you created (minted) your NFT.