The system default "profile" is /etc/profile.
Thse are called dot files "."extention to see them from the shell login in use
ls -la. Not all distro's create a .profile or .bash_profile in users home directory.
Any changes you want every user to have should be make in /etc/profile.
the genearl syntax is:
ENV_NAME=
export ENV_NAME
If you are new to Unix/Linux I would suggest that you read this Howto
before you go much furthure:
http://tldp.org/HOWTO/DOS-Win-to-Linux-HOWTO.html
As well as the howto and guides on:
http://ltdp.org