I want to ask a question in Stack Exchange with a data file. I'm new to Stack Exchange & I don't how to post my excel data file here.
I'd be grateful if anyone can tell me how to do it.
You can't upload a data file. See Jeff Atwood's answer to "Please add a system to allow file uploads attached to questions and answers".
In general, you should strive mightily to make each question (and answer) self contained. Minimize the need for data files as much as you can.