inheritance and table

hi

i don't have understand how works inheritance of tables...

if table B inherits from table A

- A and B must share primary keys?

- if i isert record in B the record is replaced in A ?

can i avoid this?

i would like to have this scenario:

table A

table B inheridts from A
table C inheridts from A

if i insert a record in B it must be insered only in B!
if i insert a record in C it must be insered only in C!

is it possible?

thanks