How does copyright work?

[kami_ryu]

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[Dolan]

You could just check with your country's authorities and see if your work qualifies under your country's specific copyright laws.

https://www.copyright.gov/help/faq/faq-general.html

https://www.copyright.gov/circs/circ01.pdf

Not everything is copyrightable (you're probably not going to be able to copyright a grocery list, for example) and not everything that is protected under one country's laws enjoys similar protection in another country.
If you are sure you will need lawsuit protection, you can register your work with your country's specific agency.

[Mr_Bramboy]

You have to do more. What exactly that amounts to depends on French and EU law. (unless you're in the States right now?) If you are serious about protecting your commercial interest then you should contact a lawyer, since copyright law is one of the hardest and most complicated fields in law. There are institutions where you can ask for free legal advice in my country, so you should google your area and find out if there are foundations like these nearby.

One thing worth mentioning is that, since you uploaded your content to Sheets, Google has the right to own your content for 'improving all Google services'. Check their terms of service for more information. The gist of it is that, by uploading your content to a Google service, you granted a limited copyright license which will never expire, even if you pull your content from Google now. So once again, if you plan on making money off of whatever you've created, keep this in mind.

Source: Law student

[Dolan]

Some kinds of works qualify under US copyright law automatically, without you having to do anything, as far as that agency's site says. But that's for typical stuff like novels, architectural plans, songs.
When you have a niche case, it might be best to consult with them (agency) or NGO.
Unless you have shekels to pay for a lawyer.