Banner's don't have to be confusing. Take a look at the ones up above and you can see some are detailed and flashy with rotating images, but must are a picture with some text.
You can go to
www.mybannermaker.com and go through the steps there to create your own, but you will need to ask whoever is telling you that you need one what size it should be. Once you know that you'll know which one to pick on that site, then you add in the picture you want and the text.
If you are still confused send me a message and I will gladly give you a hand.