Double click the layer to open layer style window. Apply settings as shown.
From layer menu select layer style>>create layers. Press Ctrl+Alt+G to unmask the shadow.
Ctrl+Click the rectangle layer thumbnail to get the selection. Press Ctrl+Shift+I to inverse the selection. Press Delete. We'll keep this layer on top.
Create a rectangle using rectangular shape tool.
Double click the layer to open layer style window. Apply settings as shown.
Similarly create more rectangles of different colors and apply same layer style.
Populate the card with text message. To spice up the card use different fonts and sizes.
Insert an image of your friends. Move this layer right above the purple rectangle layer in layer order in layer palette.
