Imagine the Offensive Line how it stands...
Then imagine a number system for placement over the O-Line.
0 being directly over the center. Also called a Nose Tackle or the big fat guy in the center of a 3-4 defense.
1 is slightly off to one of the sides of the center. This is what Mebane typically plays for us.
3 tech is to the opposite side that the 1 tech lines up on.
It is really hard to line this up in text form. Basically in a 4-3, the DL is supposed to shoot for one of the gaps between the offensive linemen. The defensive ends usually line up further off the outside of each tackle.
The Leo is a type of end that is often moved around a little, and can both start from a standing position or with his hand in the dirt. We use the Leo on the opposite side of a 5 Tech.
sometimes you'll hear a wide 9 which is where Jason Babin had success in Philly a couple years ago. It mainly helps fast DE's because they can get running around the tackle before he can get in place with his kick step.
Hopefully this helps some.
*edit* LoL found an image that does what I tried to do in text.