How do I make parameters mandatory in PowerShell?

You specify it in an attribute above each parameter like this:

function Do-Something{
    [CmdletBinding()]
    param(
        [Parameter(Position=0,mandatory=$true)]
        [string] $aMandatoryParam,
        [Parameter(Position=1,mandatory=$true)]
        [string] $anotherMandatoryParam)

    process{
       ...
    }
}