The path to your .abp is as follows:
data\art\armies\west_german\soldiers\volksgrenadier\volksgrenadier.abp
So, that means that
"..\\..\\weapons\\smg_mp44_default\\smg_mp44_default",
goes up two directories from that file, due to the use of "..\\" twice, to the root west_german folder.
Just think of it like this, for every "..\\" you see, take a folder off the current file's path (without the file name, of course):
Start
data\art\armies\west_german\soldiers\volksgrenadier\
One "..\\"
data\art\armies\west_german\soldiers\
Two "..\\"
data\art\armies\west_german\
Relative pathing just means that you use the current file's path to navigate up or down.
Going down would just be adding subfolders to the path. So, if the Volksgrenadier folder had a subfolder called accessories, with a model named panzerfaust, you would do this:
"accessories\\panzerfaust",
And that would bring you to:
data\art\armies\west_german\soldiers\volksgrenadier\accessories\panzerfaust
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