An array is used when we need to handle similar types of data. It is defined as a sequence of variable that can store value of one particular data type. To define an array, we use this guide:
type   array_name[size];
For example, if we want to make an array to enter the age of 5 people, we write it like this:
int   age[5];
The resulting array can be represented the first image of the top. 

This array has 5 elements in it, but notice that the first element in the array is age[0]. This is true for any array we create. Also, we can initialize an array at the time of declaration. This means, we can enter the data that goes in each element since we declare the array, for example:
int   age[5]  =  {12,  16,  7,  14,  10};
Example: Program to store 5 numbers entered by the user in an array and display first and last number only. (Second image on the top)

Here are masteries 11 and 12, about functions, creating them and calling them. Enjoy: https://www.youtube.com/watch?v=54p8SYCX8cY

This is mastery #22 explains when to use which type of repetition.

While: 

Now we start from zero,

and don’t try to be a hero,

repeats something as long as you want,

with that I’ll give you a hand.

You have to use a condition, 

if you want it could be addition, 

be careful because infinite it is, 

and of eaten cake it’s a piece.

For:

If you don’t wanna repeat that much,

this will help you, I have a hunch,

you just set a little parameter,

it’s not like running a kilometer.

just wait for it not to be true,

who couldn’t do this, tell me who?

Do While

Here we get to another part, 

I really feel it with my heart,

now we can set an end,

for the WSQs of Ken.

condition will be true or false,

you just can’t make no faults.

The infinity of while is gone,

don’t get me with your gun.

Here are masteries 17 and 21. Actually easy for me. I learned how to use “switch” to do this mastery and it was easy to use and useful for me. Enjoy: https://www.youtube.com/watch?v=zr2WxayvjoI