Please look at the below image:
As you can see, the right side of the image looks blurry. I've tried to use blurry filter and eraser with 0% hardness but doesn't work :( How can I achieve this efffect?
It's not a blur effect; it's just the use of a gradient.
Select a two color gradient.
Make one of the colors white and make the other one clear.
Use the gradient filler tool to apply it directly on top of the other layers.
This particular gradient is achieved using a linear gradient with the angle set to whatever you need it.
Do the above but use a white to black gradient (visible to invisible) on a layer mask instead. It's a more "controllable" effect and you do not destroy or add unnecessary layers/size to the completed file.
You can also apply this mask to a group/folder as well to cover many layers at once.