That's right, example usage could be:
+ On function "SumParameters"
: Set return value: Function.Param(1) + Function.Param(2) + Function.Param(3) (ie. the sum of the first 3 parameters)
+ Start of layout
: Set edit text to Function.SumParameters(100, 5, 2)
Function.SumParameters(100, 5, 2) would return 107 - the sum of the parameters.