We’re starting to wander out of Unreal territory and into general vector math land!
Subtract one location (vector) from the other, then get the length of the resulting vector to give you the distance in unreal units (cm).
If you need to brush up on your vector math, I’d suggest maybe checking out Khan Academy- some great free learning tools:
http://www.khanacademy.org/math/linear-algebra/vectors_and_spaces/vectors/v/linear-algebra--vector-examples#!
Take a look at the blueprint Pallete to see the kinds of things you can do with vectors and that might give you a good head start. If you don’t understand some of the terms, Khan or google can be very helpful! 
