Once you have created your survey, you can edit the content of the survey using the 'Survey Questions' option as below:
On this page you will see the current content of your survey in including text, questions and any other content.
From the 'Add survey element' option you can add content to your survey:
Add Header - Add a heading on the page.
Add Text/HTML - Add text content to your survey, including links / images and merged fields as in the Alert message editor.
Add Horizontal Rule - Adds a rule across the page for formatting content.
Add Page Break - You can set where the pages for the survey content are split by adding page breaks.
To preview your survey, to check the current layout of your survey content you can go to the 'Edit Survey' option for your survey in the list. You can then copy the direct link from the top of that page, as below, and open this in a new tab to view your survey as it is currently.
If you have then made any updates to your survey content in the admin area after opening the preview, you can navigate back to the preview tab, then just refresh that page in your browser (F5) to load any changes.