This is very useful for creating flyers and party invitations.
STEP ONE: Open a background image that you want to put type over.
STEP TWO: Using the Rectangular Marquee tool, make a selection over the area you want the type to appear. Click on the new layer by clicking on the New Layer icon in the bottom of the layers palette.
STEP THREE: Press the letter "D", then the letter "X" to set your Foreground color to white. Fill your selection with white by presing Option-Delete (PC: Alt-Backspace). Deselect by pressing Command-D (PC: Control-D).
STEP FOUR: Lower the Opacity of this layer to 80%, less if you want to create a more definitive backscreen. I generally stay between 35-60% opacity, but that's entirely up to you. Switch to the Type tool and create your type over this layer. I highlighted the text to change colors from black to white and added the maple leaf by using the Custom Shape tool. To put them both on the same layer I rasterized the type, then merged it with the maple leaf.
STEP FIVE: To add more depth to the backscreen effect, you can add a Drop Shadow as I have done in the image at left. Just click on Layer 1 in the layers palette to make it the active layer, then click the little f icon in the bottom of the layers palette for a pop-up menu of Layer Effects, and choose Drop Shadow. You can Stroke the layer if you like to create an edged border, and add an Inner Shadow to give it a more three dimensional look.