Step integrates the AMM liquidity pools of several other projects into the Step trade page. Currently that includes Serum and Orca. Step has no pools of our own. The following shows how a user may initiate a swap
Firstly you should select the currency pair you want to swap. Note the 'Swap from' field should be a currency you have a balance of. You will also need a balance of SOL regardless of the pair being swapped in order to pay fees to the blockchain.
Once you have chosen the pair you want to swap, a green 'Swap' button will appear and an approximate exchange rate and minimum amount received will be calculated. When you are ready to swap hit the 'Swap' button and the transaction will be executed.