Has anyone ever tried to design a t-shirt and sell it?

I have a good idea for a brand and a line of shirts, but I have no clue where to start. My sister told me that Etsy stole her idea, but it sounds like she had copycats. I don't know how to protect against that unless you copyright a design, which I don't know how to do yet. So, if you have any advice on this subject matter please let me know! I could use some help. Thanks!

Has anyone ever tried to design a t-shirt and sell it?
Has anyone ever tried to design a t-shirt and sell it?
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