Check out Snappa at https://snappa.io/
Snappa is a simple graphic design tool for boosting your engagement. – Snappa.
Sign up for a free Snappa account at https://snappa.io/ …this account can be upgraded for $15 a month, or $10 a month if you commit to a year.
Start off by choosing a post type or ad.
Either create from scratch, or choose to edit a pre made design, some of which will require a pro subscription.
Edit the design by adjusting the background, text, graphics and shapes.
If you would like to save a design, to finish at a later stage, you must create a pro account, however you can download your design on the free account. You can download in a number of file qualities and types, depending on your need.
Snappa has provided a user explainer video on Vimeo: