Use Polkadot.js Browser Extension to create two Polkadex accounts - one Stash account and one Controller account. On Polkadot.js app, switch to Polkadex by clicking the network symbol on the top left corner of the interface. Go to "Network" at the top tab and select "Staking". Click on "+Nominator", choose the stash account and controller account. Enter the PDEX amount to bond. Choose the destination for your staking rewards under "payment destination". Nominate "RockX_PolkaDex" as your validator.