I am going to assume you've already downloaded the pack.
Go to the location of your pack (like the folder "Downloads") and use your extractor tool to extract the .zip-file (I use
7-Zip).
Now open your map (the map where you want those models in), or create a new one.
Open the "Import Manager" (F12) and select "Import File".
Select the newly extracted folder, like this:
And continue on until you find the .mdx-files. In this example, I will pick "Fortification Big Tower".
Select the model file - not the portrait, you should ignore that for now - and press "Open".
Once that is done, the import manager should look like this:
Although I like to make my import manager look clean, so instead of "war3mapImported\" in the path name, I will write "Buildings\".
This way we can easily keep track of what category the models are in.
Now you need to assign that model to a unit.
I will give the model to a Scout Tower. To do this, go the object editor and find the Scout Tower (Human\Melee\Buildings).
Once you find the Scout Tower, you need to edit the field "Art - Model File"
Click on that field and modify it to this:
Note that you still can't see the model in the World Editor. This is normal.
However, if you place the unit on the map (it will become a colored box) and then test the map (F9), it will work in-game.
To make it work in the world editor as well, save the map, close it and then re-open it again.
(The World Editor only loads models when opening a map, not when they've just been imported).
You're done! Now you can import and use models (without texture files) with ease.