They conducted an ERC20 token sale on the Ethereum network. It sold out in seconds. The tokens (BAT - Basic Attention Token) are to be used to buy advertising in the "attention economy." The premise is really interesting, but the dynamics of the Ethereum token sale space are borderline insanity at the moment, and will continue to be until most of the fools are parted with their ether either by a company that fails or turns into a scam.
They sold off tokens which give access to advertising space in their browser, though the Etherium blockchain, and for a set amount of tokens per ETH. So they now own 35M worth of ETH, and a few entities have near-exclusive access to advertising inside Brave (but can also sell those tokens off).