take a look inside openembedded/packages *.bb and You will learn something new.
to ad something (patch, anything) You need to modify that *.bb file You are looking it.
to "executing build command" use bitbake command.
For example:
cd /working_dir/build-dm800
source env.source
bitbake package_name
to remove/clean package use
bitbake -c clean package_name