SQL & PL/SQL

Hi Experts ,

I am here to get more better understanding about this concept in laymens term please advice me on this concept , i searched in google i got tons i dont know which is right

this are my doubts :
1) i have an employee table in which i have 10 columns , here i have created view using the employees table as base
created view ttt with 3 colums from the employee table in condition emp_id = 90

when i( select * from ttt) found 3 rows selected when try to delete 1 row in the view i can able to delete ...but when i try to insert iam unable to insert

here i found when iam deleting a row in the view that row is also deleted from the base table ...

2) why do we go for view ..what is it used for ?

3)difference between view and materialized view?

so please clarify my doubts about view and tables ?plz in laymens term

why do we go for view


Thanks
Suresh