Your webmail account can be accessed by visiting your website address with "webmail" appended to the end. For example, if your website was www.xyzcompany.com your webmail site would be www.xyzcompany.com/webmail - where "xyzcompany.com" would be your actual website address.

When prompted enter your username and password

Select one of the online webmail programs. Each work slightly different and you can try both to see which you like best. Horde has more options and SquirrelMail is more simple and quick to use.