Power Automate for desktop has an Actions pane, a central flow and a Variables pane. Set variable creates or changes a desktop variable. The Variables pane shows its current value during execution, which is useful when a later action reads the wrong input. Desktop variables use percent references such as %Reference% in action fields.
A variable can hold text, a number, a list or a data table. Keep those types distinct. A text identifier with leading zeros should stay text even if you convert a different field into a quantity. In this local designer, the Test event provides the input values and Display message records a simulated dialog. It doesn't open a dialog on your computer. Use Run next action to inspect a value immediately after the action that sets it, before another action replaces it.