1. Log into webmail
2. Select Settings

3. Select the Identities tab

If you are still using the default identity, your name may be default. You should update that while you are here.

4. Click on your identity or the default identity, which ever one you are using.

5. Fill out the above information with your information and complete the signature block. Advanced EDIT:
You may include your website link by inserting an HTML link to insert the html link, use the link tool:

This icon opens the link too:


Link: your website, such as http://example.com
Target: leave set as is
Title: What you want the link to say, example: www.example.com