add or subtract days from a 'date' in query

hi all!

I'm quite new to pgsql, but I tried to read as much docs as I could, and
also tried to browse the ml archive here, without useful results until now.

So I hope you will excuse me for the following question, that I know must
appear quite tedious to the experts :))

I just need to add (or subtract) a certain number of days to a given date
(in the format yyyymmdd), but cannot find the right syntax.

I tried many ways, making a cast to date, or to timestamp, but nothing got
right
For instance, , cause I want the second date to be ten days more than the
1st, I started writing a query such as:

    insert into mytable (dateA, dateB)
        values
                ('mydateA', 'mydateA'+ 10)

but got an error msg, telling that I cannot add unknown type with int


so I made

        insert into mytable (dateA, dateB)
            values
                ('mydateA', 'mydateA'+ 10 days)

but pg did not understand what that 'days' stood for


so I tried


        insert into mytable (dateA, dateB)
                values
                    date('mydateA', 10)

and so on, but always with no result :((


Could anyone please help me?

Thanks a lot

        bubola