You must first complete your account verification before you can start staking BMEX in your BitMEX account. You will need to have at least 25 BMEX available in order to stake and enjoy the additional perks.
To stake BMEX:
Log in to your BitMEX account
Go to Wallet page (https://www.bitmex.com/wallet)
Tap Stake to land on the modal dialogue Increase staking amount
Adjust the slider to top up your BMEX Stake and review the prospective taker fee discount you can get by staking the additional amount of BMEX
Tap Learn more if you would like to see the full fee schedule
Tap Increase stake to confirm your staking amount
Your effective BMEX Stake and the fee discount will be updated immediately once you confirm
Note: The figures in the screenshots above are all indicative and for reference only.