An IF Statement

The reason you are having the results you are the following reasons:

This ...

$UList = (Import-Csv "\\SERVER\SHARE\Folder\File.csv")

... is just reading a file and storing that content that you are not using in your script for anything.

This...

$_Department

... is not populated from anything in the code you show. I am going to assume, this is in that text file, and if it is that is not the way to call it, but I am not sure since you don't show a sample of what is in the text file.

This...

Add-QADGroupMember -Identity `$A-DWN -Member Dewy.Seemore

... is using the PowerShell line continuation / termination character unnecessarily.

This ...

($_Department -eq "APD")

... is not the way to call a variable from a file.

The reason, you are getting results when you uncomment this...

# $UList

... is because you populated it at the top of the script, but again, you are not using. So, please show a sanitized snippet of the text file, for better clarity.

This sounds like you are new to PowerShell, and or that and ADDS scripting. I see you installed the QAD module, though it's a nice module, it is really not needed to do this. Just install the RSAT tools on your workstation...

Remote Server Administration Tools for:
Windows 10 - https://www.microsoft.com/en-us/download/details.aspx?id=45520
Windows 8 - https://www.microsoft.com/en-us/download/details.aspx?id=28972
Windows 7 - https://www.microsoft.com/en-us/download/details.aspx?id=7887

or use PSRemoting (explicit or implicit) and use the cmdlets from the DC.

If that is the case, It's critical that if you are new, that you first spend the time to ramp up to prevent a lot of unnecessary frustration and confusion your are going to encounter.

Do a search on Microsoft Virtual Academy on PowerShell and YouTube for no cost video training.
https://mva.microsoft.com/search/SearchResults.aspx#!q=powershell&lang=1033
https://www.youtube.com/results?search_query=beginning+powershell

Use all the free eBooks on this site.
https://leanpub.com/u/devopscollective

Read the full help file on any cmdlet you are trying to use, practice with the examples, then read the helpfile again, then pick up a few good books, like, 'PowerShell in a Month of Lunches'.
https://www.amazon.com/Learn-Windows-PowerShell-Month-Lunches/dp/1617294160/ref=sr_1_1?ie=UTF8&qid=1541490524&sr=8-1&keywords=learn+powershell+in+a+month+of+lunches+3rd+edition

There are lots of free PowerShell eBooks on Microsoft's websites.

See also: The PowerShell Survival Guide
https://social.technet.microsoft.com/wiki/contents/articles/183.windows-powershell-survival-guide.aspx

As for your script, there is no reason tp do this from scratch. You can let Windows Server write this script for you using the ADAC then you can tweak as needed.

Step-By-Step: Utilizing PowerShell History Viewer in Windows Server 2012 R2
https://blogs.technet.microsoft.com/canitpro/2015/03/04/step-by-step-utilizing-powershell-history-viewer-in-windows-server-2012-r2

Learning PowerShell with Active Directory Administrative Center (PowerShell History Viewer)
https://sid-500.com/2017/10/10/learning-powershell-with-active-directory-administrative-center-powershell-history-viewer

Or just download on from the Microsoft PowerShell Gallery.

PowerShell: Create Active Directory Users Based On Excel Input
This script will create users in Active Directory based on the settings in the input file (see the Excel / CSV file below this script for an example of the input file used). These settings can, of course, be changed or extended (check this Microsoft TechNet Link to get an over
https://gallery.technet.microsoft.com/scriptcenter/PowerShell-Create-Active-7e6a3978

Bulk Create Active Directory Users v1.5
This utility requires the Active Directory PowerShell module be installed, which is a part of the Remote Server Administration Tools (RSAT)
https://gallery.technet.microsoft.com/scriptcenter/Create-AD-Account-from-CSV-09ee9d39

You don't need write host to display to the screen, that is the default. You only need it for text coloring or other specific formatted needs. Use only single quotes, unless you are need to expand variables or dealing with special quoting needs.

In production scripts, never use aliases. They are just hard to remember, maintain, and non-descriptive. They are OK for throw away code, or interactive stuff.

Again, look at the above ADAC would produce for you (that you can tweak) and or the above samples, but all-in-all, roughly, your script should look something like this...

$UList = @'
Department,SamAccountName,GroupName
APD,Dewy.Seemore,A-DWN
123,username,group
'@ | ConvertFrom-Csv

ForEach($UL in $UList)
{
    If ($_.Department -eq "APD")
    {
        Write-Host "This is if Statement for $($_.SamAccountName)" -BackgroundColor White -ForegroundColor Red
        Add-ADGroupMember -Identity $_.GroupName -Member $_.SamAccountName
    }
    Else { "$($_.SamAccountName) is not in List"
    }
}