Canva is a great, user-friendly programme and has the standard free and paid for versions that you seem to get with everything these days. I use the free version and I can honestly say I've never found myself unable to create the promos that I want to use.
If I can't find a free image to use, I just upload a royalty-free image from somewhere like Pixabay instead.
There are lots of other tools available in Canva including their great range of pre-made templates that you can customise for your own use.
The key thing to remember with programs like Canva is if you make a mistake you can just click undo or delete or even start again. And if you finish the design and don't like it - you don't have to use it!
Let me know how you get on and if you have any questions, I'll do my best to answer them for you.
Claire Buss is a multi-genre author and poet, completely addicted to cake. Find all her books on Amazon. Join the discussion in her Facebook group Buss's Book Stop.