Pop one value and one string, set the variable of that name with that value.
If this instruction is executed inside a function and a local variable of that name exists, then that local variable value is changed (as long as the name is not a full path name.) Note that to make sure that you set a local variable, it is a good idea to use the Set Local Variable action instead.
Nothing is pushed back on the stack. Variable names can be full paths as defined in the Get Variable action.