This game runs on Ethereum test networks: Kovan and Rinkeby currently.
You need a browser extension like Metamask that you can download from https://metamask.io/download.html.
You have to connect to either Kovan and Rinkeby network. So select one in Metamask and press .
If you do not have ETH in one of the testnets above, go here to get some: https://ethereum.org/en/developers/docs/networks/#testnet-faucets.
Set the amount of ETH you bet, and press the button of your choice of hand. Then a Metamask popup appears, and after you approve the transaction, the smart contract will evaluate the hands, and send the staked amount of ETH to the winner.
For example: A player bets 1ETH on rock, B player bets 2ETH on paper. Paper covers rock. So B player wins 2ETH, because 1ETH matches 1ETH, and B player remains in the contract with 1ETH bet on paper. Then C player bets 2ETH on scissors. Scissors cut paper. So C player wins 2ETH, and remains with 1ETH bet on scissors.
Bet: ETH on