So a noun is a person, place, thing, or idea.
So if we look at the first sentence:
Her grandmother lives in the desert.
We can tell which ones are the nouns by going through each one of the words.
grandmother is the first noun, because it's a person, because a grandmother is, well, a person.
desert is the next and last noun, because it is a place.
And we can do the same thing with the next sentence.
father would be the noun because a father is a person. A lizard would be a noun because a lizard is a thing.
You can repeat this with the next sentences.
(Note: a noun can also be an idea, like something like, inspiration)