This is the link to USA Ultimate.
You will register as a player, fill out waivers, and accept team invites here.
Additionally, this is a direct link to the required medical authorization form. This will be required to have on file for sanctioned USAU events.
https://usaultimate.org/wp-content/uploads/2020/09/Medical-Authorization-V4.1.form_.pdf
This is the Colorado Youth Ultimate organization that runs the leagues and offers schedules as well as other playing opportunities.