I am creating a script to retrieve all the machine names from a .txt file then Query against them;

ComputerName UserName (Of the last person to logon to the machine) Date it was last Logged on to/Used

This is what i have

Clear-Host
$machines = Get-Content -Path C:\Users\khalifam\Desktop\Winver\MachineNames.txt
ForEach ($Compu in $machines) {
    Get-WmiObject –ComputerName $machines –Class Win32_ComputerSystem | Select 
    Username, PSComputerName | FT
}

As sidenotes:

• the hyphens for the parameter names are not hyphens, but En-Dashes, so I gather this code is copied from the internet somewhere
• inside the loop you are using the wrong variable on the ComputerName parameter which should be $Compu

Having said that, I don't think you can get the info you need from the WMI Win32_ComputerSystem class..
What you will need to do is to parse the info from the computers eventlog:

# get an array of computernames loaded from the text file
$machines = Get-Content -Path C:\Users\khalifam\Desktop\Winver\MachineNames.txt

$result = foreach ($computer in $machines) {
    # test if the compurer is on-line
    if (!(Test-Connection -ComputerName $computer -Count 1 -Quiet)) {
        Write-Warning "Computer '$computer' is off-line."
        # skip this computer and carry on with the next iteration
        continue
    }

    # search the computers eventlog and parse the username and last logon time from that
    # you can play around with other values for -MaxEvents if you feel you're missing information.
    Get-WinEvent -ComputerName $computer -FilterHashtable @{Logname='Security';ID=4672} -MaxEvents 20 | 
        Where-Object { $_.Properties[1].Value -notmatch 'SYSTEM|NETWORK SERVICE|LOCAL SERVICE' } | 
        Select-Object @{Name ='ComputerName'; Expression = {$_.MachineName}},
                      @{Name ='UserName';     Expression = {$_.Properties[1].Value}},
                      @{Name ='LastLogon';    Expression = {$_.TimeCreated}} -First 1

}

# show on screen:
$result | Format-Table -AutoSize

# save as CSV file
$result | Export-Csv -Path 'D:\LastLogonInfo.csv' -NoTypeInformation

---

Update

If I understand your comment correctly, you would like a list of all users (except for a few) and retrieve their latest login on a computer from the list.

In that case you can do the following:

# get an array of computernames loaded from the text file
$machines = Get-Content -Path C:\Users\khalifam\Desktop\Winver\MachineNames.txt
$result = foreach ($computer in $machines) {
    # test if the compurer is on-line
    if (!(Test-Connection -ComputerName $computer -Count 1 -Quiet)) {
        Write-Warning "Computer '$computer' is off-line."
        # skip this computer and carry on with the next iteration
        continue
    }

    # you do not want to include these account logins
    $exclude = '\$|SYSTEM|NETWORK SERVICE|LOCAL SERVICE|KHALIFAM'
    # search the computers eventlog and parse the username and last logon time from that
    # you can play around with other values for -MaxEvents if you feel you're missing information.
    Get-WinEvent -ComputerName $computer -FilterHashtable @{Logname='Security';ID=4672} -MaxEvents 100 | 
        Where-Object { $_.Properties[1].Value -notmatch $exclude } | 
        Select-Object @{Name ='ComputerName'; Expression = {$_.MachineName}},
                      @{Name ='UserName';     Expression = {$_.Properties[1].Value}},
                      @{Name ='LastLogon';    Expression = {$_.TimeCreated}} |
        Group-Object -Property UserName | ForEach-Object {
            $_.Group | Sort-Object LastLogon -Descending | Select-Object -First 1
        }
}

# show on screen:
$result | Format-Table -AutoSize

# save as CSV file
$result | Export-Csv -Path 'D:\LastLogonInfo.csv' -NoTypeInformation