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.