How do we add one or more rows manually( by typing row numbers).
?

Could you please explain what you mean?

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I have to insert 25 rows in between two rows (which having data) by typing inserting row numbers

That definitely doesn't explain anything.
Between which two rows?
Where are you typing those row numbers?

Here's what I'd do to quickly insert 25 blank rows between the existing rows 3 and 4.

Alt + F11 to bring up the VBA environment
Ctrl + g to bring up the immediate window
Type in Hit Enter.

Do you really need code? This can be done easily:

* Select the second row between which you want to insert
* Drag down to select 25 rows
* Right click and select "Insert".

1. Click in a cell above or below where you want to add a row.
2. Under Table Tools, on the Layout tab, do one of the following:
   • To add a row above the cell, click Insert Above in the Rows and Columns group.
   • To add a row below the cell, click Insert Below in the Rows and Columns group.