You can find order confirmation email in setting->notification
Open template and you can add you GIF or style changes, but you have to verify it because most of style will override by defaulr shopify css.
This is an accepted solution.
First you have to upload your GIF in setting->file and then copy its url, now open email template then add where you want and preview it.
You can upload your GIF in setting->file and then copy its URL and paste in email template.
Yes upload your image to file and then copy and paste url in email template.