To trade futures contracts in Bexplus, you need to deposit BTC in your account firstly. If you haven't bought BTC before, you can purchase some from references fiat-to-crypto exchanges. When you finished purchasing, you can directly deposit BTC in your Bexplus account.
Login your account
Open your account by clicking on the top right corner on the home page
Then choose either Fiat or cryptocurrency in the "You send" Box