Where you touch on the screen, the top will display coordinates. Simple as that.
Source code is all here. All of it.
Make a folder, any name is file. put the 3dsx file, the elf file, the smdh file, the makefile, and the icon file on the root on the folder. make a folder called source on the root, put the "main.c" file in there. NOW, last step is the build folder. Make a folder called build, then drag the following, "main.d, main.o ronxterb.lst, ronxterb.map" all into this folder. Put this folder with your homebrew apps and you're done!