Q: What is the main purpose of MDM Data Manager? What are the functions it perform?

A: In data manager we can do host of activities:

Creating/change/delete records.
Defining hierarchy/taxonomy table in respective modes. Linking of Attributes
Performing drill down search and free form search
Data governance:writing validations n assignments.Executing them.
Creating workflows and executing steps of workflow
Matching mode used for matching n merging of records in MDM once rules and strategies are defined.
Family Mode and Publish mode for creating catalogs.
Several others..refer to data manager reference guide for MDM.

Q: Is there an export feature in MDM Data Manager that would enable to obtain an excel extract of record details which also include validation result
columns ?

A: The export feature of the data manager, exports just the fields of the repository in an excel. However for this requirement, there can be a workaround. Create a status flag and assign it your validation result. As this status flag is now a part of your repository you can export it.