How do I name a new file in the index
You were asked to improve wording of your question, not to put it aside and create a new one. If this is indeed a duplicate of the linked question, delete one of them.
This one is not clearer than the previous one. What do you mean with “in the index”? Index in a document processor has a very precise meaning. I feel like your question is rather an OS question. So, once again, ask a good question, edit it for that and mention ridiculous information like OS name and LO version.
Hello,
File -> Save As and provide a name (and a location where to store your file)