The GeniusContacts plugin allows you to quickly and easily add a signup form for your GeniusContacts list.
You need to be using GeniusContacts email marketing web-based software to use this widget. Create new signup/subscription forms in the software by going to the "Integration" section, then they will be available through this widget.
This plugin makes it much easier to do without requiring you to know which theme (or core WordPress) files to modify. Often times copying and pasting HTML into WordPress can cause odd display issues (depending on your WordPress theme).
The same thing that would happen if they submitted it from another site: it redirects back to the GeniusContacts confirmation message, or a custom URL if you have that set up for the signup/subscription form in GeniusContacts (modify your forms under the "Integration" section).
If you enable the "Ajax" option of the plugin settings, you can have the form submitted without the page reloading (so the viewer never leaves the page).
Yes, you would just make sure that your form settings (in GeniusContacts) have the Opt-in confirmation setting checked.
Please make sure that your login information is correct, and that you have at least one Integration form already created in the GeniusContacts system.