Theory:

An auxiliary verb is a combination of Primary auxiliary and the modals.
  
Auxiliary Verb.png
An Auxiliary verb is a helping verb used with a main verb to form a verb phrase. It indicates tense, mood, grammatical aspects of the main verb.
Three primary forms of primary auxiliary verbs are : "Be", "Have", "Do"
Example:
1. Yes, I have a pen.
2. I am speaking to you now.
3. No. I did not do that.
Modals are also known as modal auxiliary verb. Modal Verbs are verbs that help the main verb to express one of the following:

Ability
Possibility/probability
Instruction
Permission
Obligation
Requests
Offer
Advice
The modal verbs are: Shall, Should, Will, Would, Can, Could, May, Might.
Some of the Primary auxiliary sentences from the lesson "Desert Animals" are:
  1. I have read a lot of information about the desert animals.
  2. So they have had to find different ways of coping with the harsh conditions.
  3. Moreover, mongooses had a responsibility to take care of their babies.
  4. You have to know about the two kinds of camel.
  5. Few snakes have to eat more than once a week.
  6. What will the desert animals do?
  7. Camels have long, shaggy winter coats to keep warm.
  8. If they have nothing to eat for several days, their humps shrink as the fat is used up.
  9. So desert animals have to find different ways of coping.
  10. The Dromedary has only a single hump.
  11. It has a speciality of poking their nose into holes.
  12. The mongoose has sharp paws and claws where it can easily scratch the ground.
  13. The Bactrian camel has two humps on it.
  14. Snake can kill a human being with just one bite.
  15. Its frightening rattle can be heard as far as thirty metres away.
  16. The snake can feel the movement.
  17. The larger pythons can survive for a year or more without eating.
  18. They have had to find different ways of coping with the harsh conditions.
A few sentences using Modals from the lesson "Desert Animals" are:
  1. Desert is the place where you could not find water.
  2. The gerbils will run away.
  3. Snakes can smell the person.
  4. The gerbils will run faster.
  5. It will coil ready to bite.
  6. You must look down the hump of the camel.