Setting a Pending Order in the MT5 Platform is straightforward.
First find and select the instrument you wish to trade on, in the Market Watch.
After doing so, you can either:
Right-click on the instrument -> New Order:
Or, drag and drop the instrument in the main page, to open its chart -> right-click somewhere within the window -> Trading -> New Order:
Whichever method you use will pop up the following table where you need to select Pending Order as the Order Type.
Once you do so, then you will need to select what kind of pending order this is as well as fill in the rest of the specifications, including the expiration date for the Pending Order.
Once all the conditions you set for the Pending Order are met, the Trade will open automatically and abide by all the specifications you set.
Note, in cases of high market volatility or else when slippage occurs, the Stop Loss function may not be triggered, if there was a sudden leap in price.