Lower Third with ALPHA CHANNEL

[#1]

I purchased a lower third motion graphic from Adobe Stock.  The creator mentioned the following - 

----There is a luma matte (alpha channel) included at the end.-----

At the end of the video, there is a short clip with a black background and white cropping in the shape of the lower third.  I've searched online and tried many versions of how to export with an alpha channel, but I think this method is unique.  Please see pics below.

Please point me in the right direction as to how to make this motion lower third transparent.  I'm certain it's simple, but haven't worked with alpha channels enough to know exactly how to make this happen.  My goal is also to separate them - which I'm sure I can do with cropping.  TYIA

i

[#2]

I purchased a lower third motion graphic from Adobe Stock.  The creator mentioned the following - 

----There is a luma matte (alpha channel) included at the end.-----

At the end of the video, there is a short clip with a black background and white cropping in the shape of the lower third.  I've searched online and tried many versions of how to export with an alpha channel, but I think this method is unique.  Please see pics below.

Please point me in the right direction as to how to make this motion lower third transparent.  I'm certain it's simple, but haven't worked with alpha channels enough to know exactly how to make this happen.  My goal is also to separate them - which I'm sure I can do with cropping.  TYIA

i

[#3]

Use the black and white image as a track or image matte on the lower third.

[#4]

Thanks for the quick reply.  I understand what the mattes purpose is, I just don't know the method of how to achieve this to make this graphic transparent.  Would you mind expanding your answer?

[#5]

Put your main video on V1, the coloured lower third on V2 and the matte on V3. Add the 'track matte' effect to the coloured third and select V3 (my still shows Track 5) in the 'Matte' option in the track matte key effects control. You may have to select 'Matte Luma' from the composite using selection box.

[#6]

Perfect!!  THANK YOU!!