Both chromosomal and point mutations occur in DNA. In what ways do they differ?

Answer 1

A point mutation occurs when there is an error in a single base pair. For example, when a sequence is mis-copied to be CAC instead of CCC.
A chromosomal mutation is a change in the size, number or organization of the chromosomes. Ex. Trisomy 21 (a.k.a Down's Syndrone) where there is 3 copies of chromosome 21 rather than 2.

Answer 2

A point mutation only involves one base pair. A chromosomal mutation involves a larger part of a chromosome: translocation, etc.