LÖVE

I'm looking for advice or any piece of information that will help me in making tiles for a top down strategy game, kinda like civ 6.

Civ3?

That's a very broad question. Having some focus to it will help you get better replies.

What kind of advice are you looking for?
What kind of experience/knowledge do you already have?
Have you made any games before?

You mean art or data? Someone else can fill you in on art, but for tiles and map data:
- for the individual tiles, you should decide what properties they need to have. do they block line of sight, what type or movement do you permit across them (flight, swimming, walking), do you want to represent the tile internally as a string (eg. for saving and loading games, or when creating maps if you are hand-making them), what is the asset you are using to represent the tile when it gets drawn in-game. I usually define this in a csv so that it is easy to add new tile types, add new properties, and get an overview of what is already in the game.
- You mention Civ 6, which uses hexes not squares. You will need to think about how to represent this data - if you had used squares or rectangular tiles you could have used a simple 2D array, but this data structure will not work as straightforwardly for a hex map so you need to do some extra thinking here.
- for games with sophisticated maps I would recommend writing your own built-in map editor, you will have faster turnaround for testing and you get the flexibility to extend the functionality as you see fit. It does take longer to get started though, so prototype your actual gameplay first before you spend weeks writing an editor.

EDIT: caveat regarding hex maps added

Speaking of hex maps, Amit Patel has pretty solid info for ya:
https://www.redblobgames.com/grids/hexagons/