Well, if you want the form to appear in your sidebar, you can use one of the sidebar widgets provided. Just go to Appearance > Widgets and play around with them there to see if you can get what you want.
If you want to add the form to a page or post (not the sidebar), then you’ll have to use a shortcode.
The basic shortcode format is [constantcontactap formid=”0″]
You just copy and paste that into the editor on the post or page you want the form to appear. Note that the first form you create gets the formid of 0, but if you create more forms, you’ll have to get the correct formid into the shortcode.
Also, be aware that if you use that shortcode, someone who signs up using the form will be added to all the lists you have in Constant Contact. I’m not 100% clear on the shortcode syntax to only add people to certain lists, so hopefully someone else can chime in and give some additional clarification on that.
Hope that helps,
-Matt