I found a techcrunch article that answers your question:

"When you place a buy or sell order, Robinhood gives you an estimated price, connects to a slew of trading venues, exchanges, and market centers to find the lowest price, and uses its economies of scale to improve to score better prices over time."

The article also mentions that wallet security and in-house funds were being worked on by the Robinhood team:

"To back-up the new Robinhood Crypto feature, the company is adding new two-factor authentication options including integrations with authenticator apps to ensure people don’t get their wallets stolen and dumped. “There are several senior world-class people that we’ve hired recently that are building the system in-house” says Tenev. Still, the move paints a giant target on Robinhood’s back. If the company gets hacked, or individual users get robbed, it could tarnish the fintech startup’s reputation."

I hope that helps! Thanks for reading and sharing your questions @blakemiles84!!