This code means the following: Once Man is collided with any other item on a scene, this item will say that it is collided with Man. That is, when event fires, inside "enter" (and "exit") statement of the block value of variable called "another item" will be equal to an item the Man collided with.
If you want to handle collisions of Man with some specific item, then inside "on collision" block you have to check if value of "another item" variable is equal to the item you are interested in (using "if" block).
Here you can find a video of "on collision" block in action. Hope that helps.