Mammals
These are vertebrates.
They are warm blooded animals.
They give birth to their young ones alive.
Most mammals are terrestrial i.e they live on land but some of them are aquatic.
They breast feed their young ones.
Examples are: Man, Lions Tiger and so on.

Animals are grouped into two

Invertebrates
Animals without a Backbone

or Spinal Column:

and

Vertebrates

Animals with backbone

Examples of Invertebrates are: Worms, Caterpillars and snakes

while, examples of vertebrates are: Man, Dog, Cat, Monkey and Lion.

this are the two main classifications of animals