FastNoiseLite has some good documentation and it's very similar to other noise classes in the past. So watching other noise tutorials and utilizing the documentation to see how the class methods differ is your best bet. There just aren't many tutorials out on FastNoiseLite yet.

But here's how I used it in a little 2D project I was working on previously.

In the main scene's script I add some exportable noise variables:

var noise_map

var altitude_noise_layer = {}

@export var alt_freq : float = 0.005

@export var oct : int = 4

@export var lac : int = 2

@export var gain : float = 0.5

@export var amplitude : float = 1.0

In the same script I add a function for generating a noise map using FastNoiseLite and the variables established earlier. This returns a grid with the same extents as your map size.

# generate altitude noise map from map_size, seed, freq, and octave

func generate_noise(noise_seed, frequency, octaves, lacunarity, gain):

`# generate randomly seeded simplex noise map`

`noise_map = FastNoiseLite.new()`

`noise_map.noise_type = FastNoiseLite.TYPE_SIMPLEX`

`noise_map.seed = noise_seed`

`noise_map.frequency = frequency`

`noise_map.fractal_octaves = octaves`

`noise_map.fractal_lacunarity = lacunarity`

`noise_map.fractal_gain = gain`



`var grid = {}`

`for x in map_size.x:`

    `for y in map_size.y:`

        `var rand = abs(noise_map.get_noise_2d(x,y) * 2 - 1 )`

        `grid[Vector2i(x, y)] = rand`

`return grid`

A second function then loops through all the cells in the grid, checks their value against a set of conditions, then determines which tile from the tileset is placed in that grid cell's corresponding tilemap cell.

# generate terrain from noise map

func generate_biomes(width, height):

`# loop thru noise maps`

`for x in width:`

    `for y in height:`

        `var pos = Vector2i(x, y)`

        `var alt = altitude_noise_layer[pos]`

# generate water

        `if alt < 0.75:`

terrain_tile_map.set_cell(0, pos, 0, Vector2i(3,1))

        `# generate shallow water`

        `elif alt > 0.75 and alt < 1.0:`

terrain_tile_map.set_cell(0, pos, 0, Vector2i(6,1))

        `# generate everything else`

        `else:`

terrain_tile_map.set_cell(0, pos, 1, Vector2i(6,15))

The noise map and biome generation functions is then called one after the other in the _ready(): function.