1. Go to https://opensea.io/ and click on the Profile Icon

2. Sign In to a wallet of your choice, I'll be using MetaMask Wallet

3. Click on Create

1. Accept Signature Request from your MetaMask wallet.
2. You should be re-directed to "Create a New Item" page

4. Upload your Item that you want to turn into an NFT

5. Add required details

6. Update Blockchain to Polygon and click Create

7. You should see a confirmation, close the confirmation.

8. To sell your NFT, click and Sell