the stage compares two  data set(after and before) and 
makes a record of the differences.
change apply stage combine the changes from the change 
capture stage with the original before data set to 
reproduce the after data set

please explain in a detailed manner

change capture stage catch holds of changesfrom two
different datasets and generates a new column called change
code....change code has  values
0-copy
1-insert
2-delete
3-edit/update

where as change apply stage applies these changes back to
those data sets based on the chanecode column