Firstly, I suspect it is sloppy coding in that the array keys "sel_model" and "Model" in the 2nd line should probably be quoted. (They may, in fact, be defined constants, in which case they would not be quoted, but I'm guessing not, in which case they are treated as self-defined constants, which while it probably works could cause problems in the future.)
Anyway, the code will create a 2-dimensional array element named $Ret['sel_model']['+2'] whose value will be either boolean true or boolean false, depending on whether or nor $tInput['Model'] is equal to Act02 (which again it is unclear here if Act02 is supposed to be a defined constant or should, in fact, be a quoted string literal).
