Do you mean you have a multi-tracked song, and you wish to apply EQ to effect all tracks together?
- insert a stereo/or multi-mono EQ plugin on your MASTER fader. Any adjustments will effect the summed signal of all your tracks.
If you mean you want to add EQ to all tracks, and adjust then individually, insert a EQ plugin (stereo or mono will depend on track) on each individual track. (that one kind of explains itself.) =)
Hope this helps.
-LIMiT