To generate the 1st date of every month in a particular cell is actually quite simple!

Today’s date is 2nd July 2014, and I have 01-07-2014 to appear in cell A1.
Thus, during entire month of July, cell A1 will have the date 01-07-2014.
In August, it will be 01-08-2014.

To get this, simply put the below formula in cell A1.

=DATE(YEAR(TODAY()),MONTH(TODAY()),1)

=DATE has 3 parts, namely
1) YEAR
2) MONTH
3) DAY

=TODAY() generates today’s date (it updates itself every day, by matching it with the current date as set in the Regional settings of your computer)

1) Thus, YEAR(TODAY()) will extract the YEAR out of TODAY(), which will be 2014 in this case.
2) Similarly, MONTH(TODAY()) will give us July (07).
3) In the DAY part, we enter 1.
This is how it will generate the 1st date of current month & year.

Similarly, you can generate every 7th / 10th / any date of the current month.

Keep Excel-ing!