Take advantage of Google Drive to create great thumbnails for your YouTube videos. In Google Slides you can easily create fantastic thumbnails. This video will walk you through how to make a thumbnail for your YouTube channel.
Check out these other videos for YouTube help:
Create Channel Art for YouTube: https://www.youtube.com/edit?o=U&video_id=cUWKV1nChNQ
How to create a YouTube channel: https://www.youtube.com/watch?v=41YehxZ7t4o&t=476s