What distribution and version of Linux are you using? There could be several different wasy to this.
As the root user, open the file /etc/profile. This will make the changes available to all users. Add these lines:
export PATH QTDIR
You will already have an "export" instead of adding your own you can just add QTDIR to the end of it. It will already be exporting the PATH variable. Just place your QTDIR and PATH statements before the export line.
The manpages should have automatically been installed in /usr/local/man. This should already be in you MANPATH You shouldnt have to set it. You can get a listing of where man looks for manpages by typing at a console prompt: man --path
For more information you can at a console prompt type: man man
The manpage paths should be set in /etc/man.config This will probably be distribution specific.
To set the LD_LIBRARY_PATH open the file /etc/ld.so.conf and add the path to your qt libraries it should be: /usr/local/qt/lib
Save the changes. Then at the console prompt type: ldconfig
This will update your ld.so.cache
You don't have to reboot for the changes to /etc/profile to take effect. Just logout and log back in too re-read /etc/profile. Or you can at a console prompt type: source /etc/profile
This doesn't seem to work on all distro's it is usually easier to just logout and login.
It is seldom necessary to reboot Linux. You don't have to reboot everytime you make a change. Not like some other operating system that will go un-named. :
If you are using an RPM or Debian based distribution all this is automated by just installing the proper packages.