This is a nice and easy exercise if you have just started using a overlock sewing machine.
This tutorial is for a 16in square cushion using a Serger sewing machine ( and an invisible zip).
Step 1: Tools and Materials
Fabric Scissors, measuring tape, pins, pen or tailors chalk, thread (colour will depend on the colour of the fabric you choose), 16in invisible zip and half a yard of fabric (Pattern/colour of your choice) and a 16in pillow insert - most fabric shops will stock all those materials and in case you're in the SF area, I recommend http://califabrics.com/ on 2109 Mission St.
Please note that, if you're planning on making this cushion in any of the TechShop locations, you will need to have passed TechShop's Industrial Serger Sewing Machine SBU.