If your powershell looks like:
param($myTestParameter) function TestParameter() { Write-Host "Parameter is: $myTestParameter" }
Saved as myTest.ps1, for example.
Then to use parameter, call script like:
. .\myTest.ps1 -myTestParameter "Test parameter"
Notice that myTestParameter is without dollar sign, and then you can call function like TestParameter, result should be something like:
Parameter is: Test parameter
Example download from here.