Do the same thing for any type of return object. Then it's a matter of knowing the type once in lisp. So if you want to return an array, this would be similar to what the coordinates property of a polyline returns:
(note, vl-sel is my own helper function to select on object and return the vl-object instead of an ename)
Command: (setq plobj (vl-sel))
Select object: #<VLA-OBJECT IAcadLWPolyline2 000000002eb94a48>
Command: (setq coords (vlax-get-property plobj 'coordinates))
#<variant 8197 ...>
Command: (vlax-safearray->list (vlax-variant-value coords))
(3244.69 8968.45 3627.96 8607.93 3537.78 8247.4 3875.97 7999.53)
Yes, this is a property which returns the value, but a method which has an out parameter will work the same way. I should also note that the quoted property or method can be either a single quoted symbol name as I did, or as a string (wrapped in double quotes)...either way works fine. (vlax-invoke-method myinstance "timestwo" num 'newnum)