A survey's fields are organized into steps. Multi-step surveys walk the visitor through one step at a time (with a progress indicator and Next/Back buttons); each step holds an ordered list of fields you add via the step editor.
Steps sit in a strip of tabs at the top of the editor - one tab per step, plus + to add one. A new step becomes the active tab straight away. Each step has two admin-facing fields (a name and a comment) that help you keep track of what the step is for; these aren't shown to survey visitors, only in the editor. Removing a step (the bin icon next to its title) removes its fields with it.
Add field opens the field catalog: types grouped into Popular, More and Content, with a search box above them. Hover or focus a tile to see it rendered live on the right, with a short description of what it is for; click it to configure it - settings on the left, a live preview of exactly this field on the right, and Change type in the header if you picked the wrong one. See Field types for every type.
Each field in the list shows its type and, where they apply, a Required chip and a Main evaluation or Main feedback chip; drag the handle on the left to reorder fields within a step.
There's no separate "one-step survey" mode or toggle — it's simply a survey whose steps list has a single entry. Nothing about the editor or the published widget behaves differently; a one-step survey just never shows the multi-step progress indicator or a Next button, since there's nothing to advance through.
A survey has one main evaluation question and one main feedback question — the fields carrying the Main evaluation and Main feedback chips. They're what later shows up as "general satisfaction" and the "default feedback text" on the Responses page.
The first numeric-scale field (rating, opinion scale or slider) you add is flagged as the main evaluation question automatically, and the first text field (long text, or a single-line one such as short text or email) as the main feedback question — as long as no other field has that flag yet. It's worth adding your primary rating and comment fields first if you care which ones get picked.
To move a flag to another field, open that field and tick Use as the main evaluation (or Use as the main feedback) on its Meta tab. A warning names the field that has the flag now; saving the field moves the flag over, and the other field loses its chip. A survey never ends up with two.
With no main evaluation or no main feedback question, the step editor shows a warning. A popup survey can't be published until both are set; inline and on-site surveys still can — see Form types.