Hi Vargeesh,
We can do this with Data Validation. When you say that "if the number is not starting with 1, it should throw a message like 'Check it'", I assume that you want a real time check while entering the data into cells.
Suppose you are working on column A. Select the entire column. Go to Data >> Data Validation >> Data Validation. Under the header "Allow:", select "Custom" from the drop down list. And enter the following formula in the field "Formula:" -
=IF(ISERROR(A1+1),FALSE,IF(VALUE(LEFT(A1,1))=1,TRUE,FALSE))
Go to the 3rd tab i.e. "Error Alert", and put "Check it" in the box "Error Message". And click on "OK" button.
During the process of doing so, click on "Yes" button on getting the following error message: "The formula currently evaluates to an error. Do you want to continue?"
After the validation is done, you should get an error message whenever you enter a number in any cell of column A, that does not start with 1. It will accept only the numbers that start with 1.