different ways to filter for CURRENT_MONTH

I have to build 2 reports:

1st report

Show all Service Requests Created in the current month.

I know I can use the CURRENT_MONTH session variable for a rolling filter without hardcoding the date range.

==> What is the syntax and how do I put it into a filter?

==> Can I use it on any date field (date/time?)

2nd report

3 columns each showing the following different numbers:

- Show all Service Requests Created in the current week.

- Show all Service Requests Created in the current month.

- Show all Service Requests Created in the current year..

For this I am using the same field 3 times and then in the Column Formula (fx) I need to use different formulae to calculate the different periods.