When a script is loaded, any parameters that are passed are automatically loaded into a special variables $args. You can reference that in your script without first declaring it.
As an example, create a file called test.ps1 and simply have the variable $args on a line by itself. Invoking the script like this, generates the following output:
PowerShell.exe -File test.ps1 a b c "Easy as one, two, three"
a
b
c
Easy as one, two, three
As a general recommendation, when invoking a script by calling PowerShell directly I would suggest using the -File option rather than implicitly invoking it with the & - it can make the command line a bit cleaner, particularly if you need to deal with nested quotes.