>>In order to purchase an altcoin such as BAT (the token behind the brave browser the article refers to), you have to first purchase Bitcoin. If you want to sell your BAT tokens, you will receive Bitcoin.
BAT is an ERC20 token on Ethereum. In order to purchase it you buy Ether, and then go to a decentralized Ethereum exchange like 0x and purchase it. When you sell BAT, you receive Ether.