Choose "Create Petition" from the "Start Organizing" menu to start creating your petition.
Fill out the petition's title, your target's name, a description and call to action for your petition to get activists to sign, and the letter you will deliver to your petition target. Finally, you can add in custom form inputs using the visual form builder (explained here) or by writing your own HTML. And you can add an optional image if you choose.
Next, you can add optional thank you page text, and show or hide the sharing options on thank you pages.
When you're ready, publish your petition to make it live and start collecting signatures.