To see how your study will appear to your participants before you set it live, you can click the Preview button in the top right corner of the study builder:

By default, the Preview will start the study from the block you're currently editing. To preview the whole study, click "Preview from start" when previewing your study.

You can also preview how your study appears to participants directly from the overview page for your study after you launch in the built in preview, or by clicking the Preview button in the top right corner of the page.