How do I pass multiple string parameters to a PowerShell script?

Lose the parentheses and commas.

Calling your function as:

$s = CreateAppPoolScript "name" "user" "pass"

gives:

cscript adsutil.vbs CREATE "w3svc/AppPools/name" IIsApplicationPool
cscript adsutil.vbs SET "w3svc/AppPools/name/WamUserName" "user"
cscript adsutil.vbs SET "w3svc/AppPools/name/WamUserPass" "pass"
cscript adsutil.vbs SET "w3svc/AppPools/name/AppPoolIdentityType" 3