Instead of awarding an affiliate commission when a sale has been completed, or a form has been submitted (both standard behaviour of AffiliateWP), Signup Referrals awards a flat-rate commission to the affiliate when the user they have referred completes a sign-up. This typically occurs when the user completes a form and creates a WordPress user account on your site.
Integrations are only shown if you have the relevant plugins installed. Likewise, when you enable an integration, a new amount field will show for that integration. This allows you to set a different dollar amount for each integration!