Scenario 1
A naive robber walks up behind you, holds a gun to your head, and hisses, "GIVE ME YOUR MONEY!" Little does he/she know, you are a matter manipulator. You simply turn around, and extend your arm towards his gun. The next second, the robber notices that his gun had suddenly turned into glass.
Scenario 2
You randomly decide that you want to destroy a building. With but a mere wave of your hand, the closest building to you would explode violently and anyone near it would get vaporized. You had essentially disconnected all of the atomic bonds in the building, causing a colossal release of energy (depending on how much force you put into breaking the atomic bonds)
Scenario 3
You notice a house that was built out of very old, frail material. It looked like it could fall apart at any second.
"Perhaps I should fix this-" you notioned. With a trivial gesture, the entire house was repaired, and it was significantly more durable than before.