In case I get you right, you should have alook at to_char(date_column,'Mon')
And this seems to be the wrong forum for the question.
Not sure to understand what you need to do,
If you want to insert new lines in your table the syntax will be something like
INSERT INTO DIM_PERIOD ( col1, col2, ... )
SELECT extract(month from calendar_date), extract(dayfrom calendar_date) , ... from DIM_PERIOD
If you need to add new values in the same record this will be an update with
SET COL1 = extract(month from calendar_date) ,
COL2 = extract(dayfrom calendar_date) ...
This forum, as the title says, is for Sql Developer questions only, not for Sql or PL/SQL questions.
Mark your thread ANSWERED and repost it in the SQL and PL/SQL forum
insert into dim_period (col_name) select new_col_name from other_table
For the EXTRACT issue just use an EXTRACT function for each value that you want. See the examples in the SQL Language doc