Make sure you are already logged into the MT4 app with your trading account number and its password.

Tap on the Instrument you wish to open on the "Quotes Tab"

Select "New order"

Choose the Volume in Lots.

Optional: you may manage your Risk Management by clicking Stop Loss or Take Profit

Optional: you may open a Pending Order by selecting Open trade when rate is, and select the price you wish the trade to open when reached.

Select the Direction of the instrument you chose, either Sell or Buy

Congratulations, you managed to open successfully a trade, you can find and monitor your open trader by going to the "Trade" tab