What it is
Website Manager → Website Builder lists system pages (Home, Give, Campaigns, Events, Stories) and custom pages. Custom pages use the AI builder. Widgets on those pages are native (same data as the dashboard content) — not iframes. Iframe embeds exist for external sites; the in-dashboard builder does not need them.
Preview stays inside the signed-in dashboard until a Main Website URL is connected and the site is published. The main site is not publicly reachable before that.
On the Main Website URL, 1 NGO keeps a consistent chrome: logo goes to site home; if a Give button is enabled it opens /give; default menu items Campaigns, Events, News point at /campaigns, /events, /stories. Extra custom links you added are kept. Subdomain surfaces (give., events., blog.) keep the header and footer you configured for those hosts.
Brand colours, logos, and header/footer are set in Brand & Identity.
What it is not
It is not a generic CMS for any industry. It is not WordPress. If you already have WordPress and want to keep it, use the WordPress plugin instead of (or alongside) a Main Website URL.