This is done as part of setting up user groups by defining the view and edit permission for each field.
This article describes each permission and what they are for.
Viewing and editing metadata
For metadata fields you can control which fields are visible (A) and which of those can be modified (B) by a group of users. There are many fields, so to make setup easier you can also click on the top check boxes or group check boxes to change permissions for all fields or for a group of fields.
Combination with edit metadata file permissions
On an individual file, metadata edit permissions for specific fields are not sufficient to allow metadata to be modified. The user also needs 'Edit metadata' permissions in a rule that matches that file. Similarly, 'Edit metadata' permissions on a rule only allow editing of those fields for which the user also has 'Edit' permission on that specific metadata field.
Usually, most groups have very similar permissions for metadata fields. Because there are so many fields, setting up metadata permissions for every individual group can be tedious. Therefore we advice to create something like an 'Everyone' group, assign that group to all users and then only set up metadata permissions on that group. Since permissions from several groups are combined, this means you do not have to set up any metadata permissions on any of the other groups.
If your metadata permission are more fine-grained, consider creating a few groups just for those metadata permissions.