@twistedxp You can read how in the Rules section here and/or the first answer in the Q&A here.
@Kuhleesee Hi! So good to see you participating! Good question, its not stated explicitly in the rules, but we'll add it to the FAQ shortly. Yes, the character in the final illustration should be visible from head to toes - all in all, roughly at least 80% of the character should be visible.
@Bailey_Walker its a good idea, and definitely would be interesting to see, but the brief calls for a only single champion. However, you can include side/support (or enemy) characters in your concept sheet or illustration.