Ref :http://www.modsecurity.org/documentation/modsecurity-apache/2.5.11/html-multipage/installation.html
Mod security works with apache. So You will have to define where is your Apache location (if you installed Apache from source)
Here I have installed Apache in /usr/local/apache Directory
Note:
Make sure you have mod_unique_id installed :
run the bellow command to make sure mod_unique_id is installed .
bin/apachectl -l | grep mod_unique_id.c
if this module is not installed [...]