Build a Banner for my FB Group

I am starting a Coaching Group for travel business owners and I need a professional banner as they're paying to join.
I have not used this site before but have used FIvver. I want something simple but eye-catching. Something that will show them what they will get, and that's it's around travel business training, not how to book travel or anything cheesy like that

I don't know what you will need to begin.