Tileset appearing in 1 box in Tile Palette

You might think I’m an idiot but I have been trying to fix this issue for 2 days and nothing has worked. When I drag my tile set into the tile palette, it all appears in the one box like this


I have watched videos on how to make tile sets, and when they chuck it into unity it works fine, I have no clue what I’m doing wrong please help!!!

In case this helps, each item on the tile sheet thing is 100 x 100 pixels, and the canvas is 500 x 340 pixels

Have you looked at the following two pages: Unity - Manual: Sprite Editor and Unity - Manual: Creating Tiles ? This would help you configure your Spritesheet and set up your Sprites as Tiles.