I’d agree with @nourishmind you should try Canva. I know that people might suggest other services as well but to be honest I have tried them and there isn’t one that it is better (and also free).
Curious to know what you are trying to design though, because Canva is pretty basic. So if you are looking to do this for professional work then you would probably want to try something a bit more hardcore.
The main one you want to use is Canva. It is great and plus it is free!
It is based around templates for different social media posts etc that you might need. So for example Instagram posts, Pinterest Pins, etc etc.
Go and check it out on canva.com
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