Deposit funds. Read How do I deposit?
Open a market, for example BTC.
Select Long if you think that the price will go up, or Short if you think that it will go down.
Enter the size, and set the leverage. Higher leverage increases your profit and your loss, and moves your liquidation price closer.
Optional: add a take profit (TP) or a stop loss (SL).
Review the order, including the fee and the liquidation price, then confirm.

Your position appears under Positions. To close it, open the position and select Close.