How do i use arrays for instantiating?

I am making a 2d runner game and i stuck here:

public Gameobject[] challenges;

void GenerateRandonChallenge{

Instantiate(challenges[Random.Range(0, challenges.Length)}, challengesSpawnPoint.position, Quaternion.identity);

}

Now my first problem is to how to make an array variable which i have declared in beginning.

Second problem is which instantiate node i am supposed to use because there are many and Thir problem is how do i get random range of the array variable and its length too.  I know how to get other stuffs but things related to instantiate and array stop my brain functioning because arrays are difficult to next to impossible in bolt. help... Lazlo I need your help this time mainly because you made this. How do i get arrays done? This is not once where i had trouble with array. I would instead suggest you to make tutorials on array of bolt instead of upgrading and development of bolt's next version...lol....