Need help on adding 3rd party library to my project file

[lansing]

My project was structured with all the *.pro and *.pri files in one pro folder, separated from the source .h and .cpp files.

build       | 
pro         | subproject1 | subproject1.pro
            | subproject2 | subproject2.pro
            | subproject3 | subproject3.pro
subproject1 | xyz.h + xyz.cpp
subproject2 | abc.h + abc.cpp
subproject3 | efg.h + efg.cpp

I want to add this KDSingleApplication library to subproject1 so I can use it.

I figured that I should include the KDSingleApplication.pri in my subproject1.pro, but then where do I put the library's source folder? And the source folder also has a src.pro, do I break apart the pri and pro from the library folder and put them into my pro folder like this?

pro         | subproject1 | kdsingleapplication | KDSingleApplication.pri
pro         | subproject1 | kdsingleapplication | src.pro

And also where should I output the build debug/release dll? I'm confused.