Well if you're talking about MAKING a banner, people usually use Photo-editing programs, such as Photoshop (most common and the best), Paint.Net (free), Paint (on every PC, I don't recommend this one though, too basic), Photoscape (free)...and more. آپ can Google 'Photo editing softwares' and you'll find a lot of free ones to download.
And if you're looking for making quality banners, آپ might wanna watch tutoring ویڈیوز (can go to Youtube یا just Google it), they'll دکھائیں آپ how to do specific things and obviously you're gonna have to fiddle with the program for a while if you're not experienced.
link is an example of Photoshop video tutorials ppl make. and link is a video teaching آپ how to create a simple banner using Photoshop. Once again, 'Google' and 'Youtube' have basically everything!