How do I get a node based on id in custom content type?
This is exactly what the node references field modules do. For example in your Article content type, you would create a new field 'Related to References' as a node reference field and link it to relevant nodes of the References content type. The field stores the title of the referenced node and its NID which makes it a lot more user-friendly interface than using a nid.

If you're using Drupal 7.x, the current recommendation is to use the Entity Reference module which takes over from the Node Reference module in CCK.

If you're using Drupal 6.x., you want to enable the Node Reference field which is part of the CCK module. This still leaves a migration path to 7.x by upgrading to the 'References' field module, and then migrating your reference fields to Entity Reference fields.