What are the roles of the "PACKAGER" in a digital rights management system?

Encrypting the original content from the creator is a packager's main job, yes.

There's a few more things it typically does:

• Add a "DRM header" to the content itself. This is usually an unencrypted blob (can be text or binary) that provides DRM-related metadata about the content. For example, the URL where the DRM client will need to go to in order to retrieve the DRM license, or the "content ID" from the DRM system's point of view.
• Interface, via an API, with the license server. This is because both the packager and the license server will need to share key material.

There's more to packagers, which is however not germane to this question... for example, they can be standalone or they can be part of an encoder toolchain. If you need to know more, I recommend you ask a separate question.