In order to sell NIL, you first need to connect to the Uniswap Exchange using your ERC20 Wallet. Once connected you can swap NIL for WETH. WETH (Wrapped Ethereum) is a commonly used token on Uniswap since it is built on the Ethereum Network.
Once you have WETH in your wallet, you can then transfer it to a centralized exchange like Coinbase to sell for US Dollars.
The process is multiple steps and typical for cryptocurrency.
What you need to setup to be able to Sell
There are a few things you need in order to buy and/or sell NIL.
Setup an account on a centralized exchange like Coinbase. This may require time to be approved. Once approved you can transfer US Dollars into Coinbase to be used to buy cryptocurrency.
Convert the US Dollars in your account to WETH (Wrapped Ethereum).
Send your WETH to a ERC20 wallet like Metamask or Coinbase Wallet.
Connect your wallet with Uniswap Exchange to buy NIL.
Once you swap WETH for NIL, the NIL will be in your ERC20 Wallet (Metamask).
When you are ready to sell your NIL, you will simply connect to Uniswap and swap NIL for WETH.