Step #1: Creating the Graph
Choose the Pie Graph Tool, click on the Artboard, then enter 450×450pt.
Step #2: Data Table
Your graph data table will appear. Enter 15, 55, 30 and then click on the check mark to apply changes. Close the data table.
Ungroup or break the graph into parts in order to apply colours and effects to each individual piece. Select the graph, navigate to Object > Ungroup or press Ctrl+Shift+G to break-up the graph into individual parts. There will be a warning box with this message: After ungrouping you will be unable to access its graph style, its data or change its graph designs. Click Yes. Now Ungroup again to break the object into pieces. Fill with any colour and remove the stroke colour.
Step #3: Applying Extrude & Bevel
Choose any piece and open Effect > 3D > Extrude & Bevel.
3D Extrude & Bevel option
Expand the window by clicking on More Options. Now you may drag the cube on the left to specify the Rotation or enter the X-Y-Z Axis values manually. Enter 20pt for Extrude Depth. Add one Lighter by clicking on the New Light icon and drag it as shown below.
Step #4: Making a Graphic Style
After selecting the yellow piece go to the Graphic Styles palette, click on the New Graphic Style icon. If your Graphic Styles palette is not visible, then open Window > Graphic Styles or press Shift+F5.
Step #5: Apply Graphic Styles
Now, choose the orange and green piece, click on the Graphic Style you’ve created in the previous step to apply the styles to the orange and green piece.
Step #6: Final Result
Notice that after applying the Graphic Styles, the pie is off a bit. So use the Selection Tool and put them back together. Now you have a nice colourful 3D pie graph.