When I make thumbnails I use a great online tool, that is easy to use, has many options to create powerful thumbnails and IT IS FREE!
It is called “custom-page.com”.
First make a free account. Be careful, they have paid services, too, but we don't need those for our purpose.
But you will need a Youtube account, no matter if you are creating thumbnails for Youtube or your website.
This is what you see when you go to custom-page.com:
When you have set up your custom-page account, log in and go to „Video Thumbnailer App". It will look like this:
You can either click on “Login with Youtube” or on “Get started now”:
Either way you will have to accept “offline access”!
Choose a light or dark template and add your image (As I already have quite a few thumbnails, my page looks different than yours):
Use the many tools to polish up your image and add your text:
Save your thumbnail on your computer. You have to choose a folder for saving the thumbnail:
The next step will teach you how to upload the thumbnail to either your website or your Youtube channel