how to submit the webform to gmail account

Break up your thing and do one by one.
1. Design a webpage that has all the fields you need to gather data for
2. Posting the data to server is a simple button click form submit and a handler on server side
3. Get all the data on server side and prepare email content
4. Send an email as per need.

Based on above, you might need help for email. Following will help for email:
Use ASP.NET to send Email from Website[^]
Tutorials on sending Email in ASP.NET[^]

Have a look at this tip too: Sending an Email in C# with or without attachments: generic routine.[^]

Go through this article:
Send Email in ASP.Net 2.0 - Feed back Form[^]

I hope it will help you.
Good luck.