Go toDefina suishswap and connect your wallet. Make sure that your wallet is connected and the Polygon Mainnet is selected.
Enter the amount of $FINA and $MATIC you want to deposit. Approve both, BentoBox and the $FINA token. After that you will be able to deposit.
After adding liquidity, you will receive Sushi LP Token, also known as LP token. You will need that token in the next steps.