Since there are lots of mobile users, I mostly recommend Ibis Paint which is the software I used to create this guide, you can follow this guide more efficiently if you use Ibis Paint (it's also very reliable)
Before making a concept, creating the concept itself in your head before drawing/modeling it is always the great choice, so don't rush, there are whole 2 weeks ahead on you. Also, Marija has mentioned it but I'll mention it again anyways: don't be a douchebag and use AI to generate nonsense, and don't even try to fool someone, There's an aged technical artist in front of you and I can understand if you're lying or not in pikoseconds
Goodluck to everyone