Leverage represents how much more you can buy than the given margin (collateral). A 3x leverage, means that you can buy 3 timex more than the collateral.
If you put in 100$ as collateral, you can purchase 300$ worth of futures contracts. For 50x the maximum purchase value would be 5000$ based on 100$ collateral.
Be very careful when selecting the leverage level. The higher the leverage the higher the risk of getting liquidated. Leverage trading involves high risks. DMEX is not responsible for any funds lost due to bad trading decisions.