If you are looking to buy NIL. Select WETH or ETH in the top pull down so you can swap your WETH or ETH for NIL.
After you select WETH or ETH, you click on Select a Token on the bottom pull down menu. Since NIL is not in your list (yet) - you need to Past the Contract Address in to the form to load the NIL Token.
The Contract Address is 0x0eb638648207d00b9025684d13b1cb53806debe4
Once you past the Contract Address - 0xD31B00deA80cF282aCE1791D204d76a85Fb82556 - into the field, you will see NIL show up as an option. Click on the NIL option.
The next step once you have the two fields ready is to put the amount you want to swap. And then click SWAP. You will see a popup like below to confirm the swap.
Set Slippage Tolerance to 18%
After you confirm the swap, it will load your Metamask (ERC 20) wallet and finalize the swap.