Download After Submitting Email

Hello WP,

I don’t know whether the question is valid in here or not. But this is such a lovely community that they don’t mind.

My Question:
I have seen many of the Blogs and Pages shows a widget on the right side normally to submit an email and get the ebook etc.

How is it done.

I mean to ask user to submit there email and after they submit there email they are able to download the file etc.

Thanks.