Redirect to a content page after login only from that page
Hope this will give you, 

In Drupal 7, you can achieve it by using destination parameter.

Just add the destination parameter in the URL where you want to redirect it.

For example if you are in login page and after login if he want to redirect to some node say about page then

YOUR_DOMAIN/user/login?destination=about


Just add the destination parameter in "To create content, you must first log in" link. On click of this link it will redirect to User login page with the destination parameter. After login it will redirect to the path you have specified in the destination value.