For more info on how to use this on a page, take a look at this article.
Using placeholders
When using our design editor while creating a personalization on a page, you can enter a placeholder anywhere in the page. This placeholder will be replaced at runtime. You can inject the default available keys or one of your custom set keys. The format for the placeholder is: {{key}}. You can also specify a fallback in the placeholder like this: {{geo.city || 'your town'}}.