The record identifier can be included in the redirect string using %s placeholder. For example, if a form is used to create a new record, and you would like to redirect to a page viewrecord afterwards, then the new record identifier can be passed in the query string:

{% form mode="create" ... redirect="/viewrecord/?id=%s" ... %}

At runtime, %s placeholder will be replaced with the record unique identifier.

Note that the placeholder works for both new and existing records.