How to create a Function using Powershell

I need help with the code below. I want the script to perform the following: prompt the user for an AD group name, if the group name is found, export the group members to a CSV file. one of the requirements is that I must include a function statement. Thank you in advance.

The code works if I use a variable like the following example: $groupsusers = Get-ADGroup -Identity $nameofgroup, instead of the function statement. However, I don't want to use a variable, I want to implement a function statement.

$prompt = "Enter A Group Name"
do
{
$nameofgroup = Read-Host $prompt
}
until(!$(dsquery Group-Object $nameofgroup; $prompt = "Group 
'$nameofgroup' was not found, try again"))

$nameofgroup = Read-Host $prompt

function GetGroupInfoToCsv (#what parameters go here?){

ForEach-Object{

$settings = @{ Group = $_.DistinguishedName; Member = $null }
$_| Get-ADGroupMember |
ForEach-Object{
    $settings.Member = $_.DistinguishedName
    New-Object PsObject -Property $settings
}

}

}

GetGroupInfoToCsv | Export-Csv .\GroupMembers.csv -NoTypeInformation

Solution

You could combine the asking for user input and returning the info into the same function. Something like this:

function Get-GroupMembers {
    $prompt = "Enter A Group Name. Press Q to quit"
    # create an endless loop
    while ($true) {
        Clear-Host
        $answer = Read-Host $prompt
        # if the user has had enough, exit the function
        if ($answer -eq 'Q') { return }

        # try and find one or more AD groups using the answer as (part of) the name
        $group = Get-ADGroup -Filter "Name -like '*$answer*'"
        # if we have found something, exit the while loop and start enumerating the members
        if ($group) { break }

        $prompt = "Group '$answer' was not found, try again. Press Q to quit"
    }

    # you only get here if Get-ADGroup found one or more groups
    $group | ForEach-Object {
        # output a PSObject with the properties you are after
        $members = $_ | Get-ADGroupMember
        foreach ($member in $members) {
            [PsCustomObject]@{
                'Group'  = $_.DistinguishedName
                'Member' = $member.DistinguishedName
            }
        }
    }
}

# call the function
$groupinfo = Get-GroupMembers
# test if the function returned anything. 
# the user could have cancelled of the group had no members to output
if ($groupinfo) {
    Write-Host "Adding $($groupinfo.Count) items to the CSV file"
    # without -Append, you would overwrite your CSV file..
    $groupinfo | Export-Csv .\GroupMembers.csv -NoTypeInformation -Append
}
else {
    Write-Host 'Nothing found..'
}

As you can see, I have changed the function name so it complies with the Verb-Noun convention in PowerShell.