Log in with your Google acount. Note that Gmail, calendar, Google docs and sites are accessed with the same login (this is Google Apps). If you want to access Calendar directly, try

http://calendar.google.com

and then log in. To create the embed code, you need to go to Settings>under Sharing>Share this calendar>Calendar Details. Note that Google's Help here is incomplete (this command does not appear on the Settings page itself):

• Copy the iframe code displayed in the 'Embed This Calendar' section.

You can also get to Details by clicking on Settings then the name of the calendar (default is your e-mail address).

While you're in Sharing, you'll need to make the calendar public.
In the Details page, you can customize the look of the calendar a bit (link is beside the iframe code).
Question 1: If you reduce the size, the font is too large. How can you fix that?
Question 2: I added a background photo and a weather calendar to the embed, but they didn't show up outside of Google (but the Holidays did). Any ideas?