Firstly, choose the size of what you want your signature to be. I'm not sure of the exact guidelines on here about signature height and width, but obviously don't over do it by creating something 1000 pixels x 1000 pixels! It will normally ask what size you wish for your signature to be when you create a new image, so enter the values here.
Then it's just a case of applying what you want to your signature. Do you want an image/images of coasters? Or maybe a skyline of a location or even artwork. Search the internet for relative images that match your desire or use your own. Copy and paste them onto your signature, and then move them around or resize them to your wishes. Just be creative I guess. There are bound to be guides on using said software floating around on the t'interweb if you get stuck on using some features.