Hello Katerina,
By default Drupal gives you options to grant access by content type. so all the nodes of a content type will have the same access. If you want to grant access by node, I suggest one of the following ways:
- Content Access Module: It has more features than any other module that does the job but it is not covered by the security team of Drupal neither has a fully stable version yet. Hopefully it will be
- Nodeaccess module: it is simpler than the content access module with less features but it is in a stable state.
- Permissions by term solution: It is more complicated to set up permissions in this case and I have analysed it in this post. However it provides more flexibility since you configure the different access.
Yes you can define the permissions now
Konstantinos