Use the Paint tool to select tiles and then paint them onto the tilemap.
Select the Paint tool from the toolbar, or press its shortcut key B.
Select a tile from the Tile Palette window and paint it onto the tilemap in the Scene view with the Paint tool. To paint with more than one tile, hold and drag the Paint tool over multiple tiles to select them all, then paint with them.
To select tiles that are on the tilemap instead of the Tile Palette window, hold Ctrl to temporarily switch to the Pick tool and pick tiles on the tilemap. After selecting the tile(s), release Ctrl to return to the Paint tool and paint with the selected tiles.
To erase tiles, hold Shift to temporarily switch to the Eraser tool and select tiles on the tilemap that you want to remove. Release Shift to return to the Paint tool**.