AssetDatabase.CreateAsset
static function CreateAsset(asset: Object, path: string): void;
static void CreateAsset(Object asset, string path);
static def CreateAsset(asset as Object, path as string) as void
Description

Creates a new asset at path.

You must ensure that the path uses a supported extension ('.mat' for materials, '.cubemap' for cubemaps, '.GUISkin' for skins, '.anim' for animations and '.asset' for arbitrary other assets.)

You can add more assets to the file using AssetDatabase.AddObjectToAsset after the asset has been created. If an asset already exists at path it will be deleted prior to creating a new asset. All paths are relative to the project folder. Like: "AssetsMyTextureshello.png".

Be aware that if adding multiple objects to an asset, the order in which the objects are added does not really matter. In other words, asset will not be special within the asset and not be any form of "root" to objects added later. The object displayed as the asset's main object in the project view is the one that is considered most important (decided based on type) within the collection of objects.
	@MenuItem("GameObject/Create Material")
	static function CreateMaterial () {
		// Create a simple material asset
		var material = new Material (Shader.Find("Specular"));
		AssetDatabase.CreateAsset(material, "Assets/MyMaterial.mat");

// Print the path of the created asset Debug.Log(AssetDatabase.GetAssetPath(material)); }