Manual mode is useful at debugging. In manual mode you can test a program or its part where a hardware variable is connected, or where we need a function block to provide a particular value.
In the debugging mode, right click a variable in the ladder and select Manual mode.
Select the Controller where the variable is located, and check Manual mode.
After confirmation, the variable is marked in yellow, and its value can be entered manually.
Similarly, the manual mode can be cancelled.
Another way to activate the manual mode is in the Variable browser. Right click a variable and select Manual mode.
The variable is marked in yellow.
Another useful feature is setting the block outputs on manual. When debugging, right-click the function block and select Manual mode.