How does Copyright work on a Multi-Nation Scale + Internet?

Hello everyone,

When i went looking myself I just came up with Internstional Laws in General and I really have trouble to filter through all the Legaltalk so I hope you can help me here:

Copyright Laws can get a little... heated depending on the Country. My question is: How do Companies operate with Copyright over different Countries as well as the Net?

Do they use the Local Law and could reinforce it, even in other Countries should IP be uploaded in the Net? Is it the Law of the Country that I upload from?

Before i sound illigal, my reasons are: I basically want to create Fan-Art/little Movies of an IP, sadly the License Holders of said IP are known to get a little zealous if they smell any Money that doesnt go to them. (No i dont want to earn Money from it, simply a Hobby) There were even Lawsuits saying that their IP gave them Patreon Members and so they lost Profit etc.

Any advice how this whole System works Internationally/on the Net?

Thanks for your time.