S = Substitution: a direct substitution of technology in place of paper/pencil, no other change; typing a document instead of writing with pencil
A = Augmentation: a direct substitution but with a fundamental change; use Google docs to type paper and share it with someone.
M = Modification: technology makes a significant task redesign; use a wiki to have a discussion around a concept
R = Redefinition: technology allows for a creation of completely new task formally unable to do without technology; using Google Earth to create a virtual field trip.
There are many examples of using SAMR on the Internet. The following is a good video sharing what SAMR is.