Now, the question is, how do I implement this with a script????
It's not just about writing OBJECTIVE_ACTIVE, right??? Is that correct?

I would set a trigger on touching the shipyard (disable the shipyard itself). Then, a window pops up (Cancel/OK), just like when you normally visit the shipyard. When you click OK, resources are deducted (I don't know how), the object-ship with a scripted name is moved, and the "Build a ship" quest is completed. If this option suits you, I'll try to write the script.

To do this, give the shipyard a name ('Name' in the properties tree), place a ship on the map, and also give it a name. Write both names here.

That's exactly the problem – I've already figured out everything, but I don't know how to do most of it!!! So, if you don't mind, I'll ask you questions so that later I can explain and help others, just like you're doing now!

You'd better explain what should be in the script part. That is, the hero goes there, does something, and we reward him by completing the quest/mission. And so on.