Go to the free online tool Canva
From the upper right-hand corner, choose ‘Use Custom Dimensions’ and put in 1920 x 1080. This is the exact dimensions of what YouTube needs for your thumbnail so it will fit in the frame perfectly.
Drag your image onto the browser with Canva and it will upload.
Click on your image and drag it into the frame. You can adjust your image size – I always like to overlap the edges by just a little bit so there’s no white space.
For myself I like to use a transparent colored shape to give a bit of definition. Then I put on my text. There’s also free images you can use with Canva (and some which are available for $1), so in this case I decided to use a Youtube play button so people can quickly see it’s about Youtube.
When you’re done, click ‘Download’ from the upper right hand corner.