These steps are for MT5 on desktop. Menus differ in the web and mobile versions.
Open the order window: right-click the instrument in Market Watch and choose New Order, or press F9.
Check the instrument and enter the volume in lots.
Add a Stop Loss and Take Profit if you want them. Leave them at zero to skip them.
Click Buy or Sell.
The window shows whether the order went through. Your new position appears in the Trade tab of the Toolbox.
If your Stop Loss or Take Profit is too close to the current price, MT5 shows "Invalid stops" and doesn't send the order. Check the stops level in the instrument's Specification.
Risk warning: CFDs are complex instruments and come with a high risk of losing money rapidly due to leverage. Only trade with money you can afford to lose.