I have copied the following for you from ‘Practical English Usage’ Item number: 168:

” There several possible ways to write the day’s date. Some peole put the month before the day; others put the day first. Commas are possible before the number of the year.

March 21st 1970 21st March 1970

July 2nd, 1936 2nd July, 1936

Some people leave out the letters (–st, –nd, –rd, –th) that follow the number.

October 1, 1932 5 July, 1966″

AND from ‘Current English Usage’ p 67:

“Dates may be written in any of the following ways: 17 July 1981; 17 July, 1981 [Note the comma]; 17th July 1981; July 17th, 1981”

The end of quote.

I prefer using the letters (–st, –nd, –rd, –th).

I hope I have helped you.

Your question is not very clear. But, I will answer what I think you are asking: The “th” after some numbers is used with dates and street numbers. The 15th of the month. I live on 15th Street. It is our 15th anniversary. This is the 15th time I have been here. You would use the number 15 (without the “th”) when you are stating things like: I am 15 years old. There are 15 items on this menu. We have room for 15 people at this table. I don’t know if this answered your question, but, it was as close as I could come to what I think you were asking. I was a little confused.

you use 15 when you write the month first (for example: October 15, 2007). you use 15th when you write the date before the month (for example: 15th October, 2007).

if you’re dating a report, you write “september 15, 2007” at the top of the page. if you’re writing about a date, then you write “on september 15th…..”.