Explanation:
(a) Main stages of mitotic division:Prophase -

Chromosomes appear as two threads/chromatids
chromatids are long thin and/later become shorter and thicker; and joined together at the centromere; the nuclear memberane; and the nucleolus disappear
spindle fibres form in the cytoplasm; with a pair of centrioles; one at each pole.

Metaphase:

spindle formation is completed
the chromosomes are arranged at the equator of the spindle
attached by their centromeres; centromeres divide; and begin to move apart. Anaphase
The paired chromatids are pulled apart/separated
migrate/move towards opposite poles
spindle fibres shorten; chromatids reach the poles.

Telophase -

Fibres disappear, nuclear materials and nucleolus are formed
bounded by nuclear membrane
the cell constricts
to form two daughter cells.

(b) Importance of mitosis:

Promotes cell growth
replacement/repair of damaged tissues
basis of asexual/ vegetative reproduction
produces genetically identical offspring
which are identical to the parents
maintains the diploid number of the chromosome of the cell.