First, it's important to note you can always try the design tool even outside of the contest using our free 9" x 9" workspace. Once the contest starts you can use a large canvas for your entry.
The general layout of the design tool looks like this:
Along the left side you'll find tools for selecting, manipulating, drawing, and erasing shapes. Along the top you'll find tools for selecting fabric, fill tools, color/fabric picker, and fabric swapping. In the top right are your zoom controls as well as text boxes for your X/Y position and Height/Width, which can be helpful for fine-grained control if you need it.
All of the buttons have tool-tip help boxes that show when you hover, I highly encourage you to read up on what each tool does and feel free to use that free 9" x 9" workspace I mentioned to just play around and get the hang of how the different tools work.
For more in-depth help, there is a series of videos showing how all of the major functions work. You can find these on the Threadbias.com website here. We also have a support forum where you can ask questions and myself or anyone else in the community can help answer.
Once the contest starts on June 27th, you can enter the contest by visiting the Quilt Design Tool page on Threadbias and in the initial getting started pop-up there is a spot at the bottom for contests. Select the Imagine This! Quilt Design Contest and optionally change the default size (90" x 108") of your quilt. Use the design tool to create your entry. You can save as you go and come back in multiple sessions to work on it. Once you are happy with your design and before the end of the entry period on July 14th, enter the context by choosing the Enter Contest option from the Contest Menu. Soon after you'll see your entry in the list of entries on the contest group page. If for some reason you decide to withdraw your entry you can choose to delete the entry using the Contest Menu.