Robinhood Chain is an Ethereum L2. If you have used any wallet before, you already know how to do this.
Use the Robinhood Wallet and it is already there. For MetaMask, Rabby or anything else, add the network manually with these details.
Once the network is added, switch to it. Your address does not change: the same address works on Ethereum, Arbitrum and Robinhood Chain, so anything that reaches you does so without you doing anything.
Fees are paid in ETH and they are tiny, well under a cent per transaction at current rates. Bridge a small amount over from Ethereum or another L2. You genuinely do not need much.
Open the DEX, and paste the contract address rather than searching the ticker. The pair is RDDT, the tokenized Reddit share, so a swap routes through Reddit stock rather than ETH or a stablecoin.
One rule
These two always show the same address. Anything else is fake.