Add a button and attachment controls in the screen.
In Upload button write the code now.
First identify that any item is uploaded or not. It means here attachments control maintains a Table.
Say that attachments control name is: DataCardValue15_1.Attachments
Now use CountRows(DataCardValue15_1.Attachments) > 0 so that it will know that an attachment is uploaded.
Now use this:
(Right(First(DataCardValue15_1.Attachments).Name,5) = “.xlsx”)
Now in button write this complete code.
If(
CountRows(DataCardValue15_1.Attachments) > 0 && (Right(First(DataCardValue15_1.Attachments).Name,5) = “.xlsx”),
Notify(
“Correct file”,
NotificationType.Success,
5000
),
Notify(
“Its not an excel”,
NotificationType.Error,
5000
)
)
Onetidbit 
Actually I create a screen called Admin, he need to upload a questions in student question paper.For tht admin need to select a attachment in tht attachment all questions and answers column is presented.what I want to do is whenever he click the attachment tht questions and answers( present in Attachment) added in student question paper screen how to do tht please explain
Hi Sorry for later reply. You still working on this solution or is it completed