There is more than one way to do so...
The first method:
Click New order at the top of the platform
The following window will appear, then you can choose the instrument and set the parameters like the volume, stop loss, and take profit.
The second method:
Double-click the instrument you want to trade from the market watch window..
Then the order window will appear, where you can set the parameters like the volume, stop loss, and take profit.
The third method:
You can use the instant trading tool shown on the top left of the chart.
Click the icon as shown in the image above, and the following panel will appear:
In the specified field, set the volume, and simply click Sell or Buy.
In your first use of this method, a window will appear that explains how this panel works. After agreeing to the conditions, you will be able to use it.
If you can't see this icon, in the toolbar go to "Charts", then "Properties", then you can tick "Show quick trading buttons", then click "Okay".