The tar ball only contains two files, the ARAGORN source
(aragorn1.2.38.c or similar) and a man page (aragorn.1). 
Uncompress with:

tar -xvzf aragorn1.2.38.tgz

Compiling example:

gcc -O3 -ffast-math -finline-functions -o aragorn aragorn1.2.38.c

Put the aragorn man page in a directory read by the man command. 
These directories may be listed by:

echo $MANPATH