Beginner tutorial for 2D tiles/tilemaps?

Hi gang. Beginner here. I've successfully completed the Create RPG tutorial and mine runs perfectly. I want to start creating my own adventure with my own graphics.

Is there a tutorial which shows how to create tiles and tilemaps? I follow the steps in the Unity manual and get as far as "Provide a name for the Palette and select the Create button. Select a folder to save the Palette Asset file. The newly created Palette is automatically loaded". That I can do. The window is now supposed to say "Drag Tile, Sprite or Sprite Texture assets here." This text does not show up and I cannot do anything. Totally frustrating.

I've watched a few YouTube videos but haven't found one that shows how to do those things. I would like to A) create a tilemap in Unity, or, B) create one in Photoshop and import it.

A quite good video I watched features apps 'Tiled' and 'Tiled2Unity' or something like that. Is this how it's done?

Are there tilemap templates floating around anywhere?

Thanks in advance :)