How to activate some flag field when create a content?
Consider using the Conditional Fields module. Excerpt from its project page:

Conditional Fields allows you to manage sets of dependencies between fields. When a field is “dependent”, it will only be available for editing and displayed if the state of the “dependee” field matches the right condition.
When editing a node (or any other entity type that supports fields, like users and categories), the dependent fields are dynamically modified with the States API.
You can, for example, define a custom “Article teaser&quot; field that is shown only if a &quot;Has teaser&quot; checkbox is checked.