If that is is all the script does, then it is a subscript, called by other script(s). It just sets those values of the current window into "global" Variables (read about the Set Variable script step in the Help). Another script likely uses those values to set the bounds and/or position of another window (likely a new window). The 2 dollar signs $$ indicates that these have global scope, which means that they persist for the current FileMaker session; which also means they must be reset before use if you want current values.
You can also just use local variables, within a single script; in which case they'd have a single dollar sign. Local means only for that script.
Thank you!... yes its a subscript indeed