Many, many Etsy sellers have difficulty when creating their own banner, which is why many sellers (me included) offer professional banner design. But - I do realize that this might not be worth it if you are just starting out.
I've taken the liberty of coming up with some easy designs, incorporated them in Powerpoint and added them to my website. They will be slightly blurry and nowhere close to what I usually do, but that's Powerpoint - but they do look good enough to get started.
You will find the designs below (all with prepared text fields); this is how you can use them.
1) Right-click in the one you like and select "Save target as..."
2) Save the Powerpoint file to your computer
3) Open with Powerpoint - add your company name & change the font
4) If you want to add a product, go to Insert-> Picture from file
5) When adding a picture, be sure to choose a design that allows for that
6) When you are done, go to "Save as...", then select GIF from the dropdown menu
7) Go to Your Etsy, Shop Appearance, and upload the new banner from your computer