say you have a script that looks like the following:
;Name of unit
_unit = _this select 0
;Name of weapon
_wpn = _this select 1
......
and you want to use that script on multiple units in your mission then you can use parameters in your init line.
[loon_one,"BAS_JM4ACOG"] exec "myscript.sqs"
would, when used on the above script make _unit equal to the name loon_one and make _wpn equal "BAS_JM4ACOG".
another instance is:
[sodding_idiot,"M16"] exec "myscript.sqs"
where _unit = sodding_idiot and _wpn = "M16".