The bad news is I can’t see any way you can import contacts from your iPad into webmail. The good news is every time you send an email via webmail it automatically adds the address to your contacts.
Edit: I should have said why don't you set the email account up on your iPad and then you won't have the problem.
Webmail is simply a portal to view your email on from any internet connected device in the world. You can also set up your email so that it downloads to one device or multiple devices. Using webmail in combination with a desktop, laptop, tablet or a mobile phone is something many people do.