Canva is a free tool (at least to a certain extent).  Free unless you want to use some of their

• Click on "Create a Design"

• Choose a template:  In this case, we're just typing "Twitter" in the search bar, and then choosing "Twitter Ad" 1600 x 900 from the resulting list

• On the uploads tab, upload your graphic(s) and sound files.

...And basically that's it.  

If you have anything you'd like me to clarify or add, please reach out to me:

via DM on X:  https://x.com/Pcast_ol

or Blusky:  https://bsky.app/profile/pcast.overlordshop.com