The Perlin object inserts a perlin noise pattern in your scene.
In the Objects tab, double-click on the perlin icon or click it and draw where you want it on the edit area.
The perlin texture has a default size and color. You can drag and resize the object and it will repeat. Right-clicking the object and selecting Edit will let you change the specific settings for the texture.
Texture width/height
Random seed
Frequency
Iterations
Density layout
Color 1
Color 2