To manage the tags for references:

Select the references and select Add Tags. You can associate the selected references with an existing or new tag or remove their association with a tag.

When the Tags tab in the Navigation area is expanded, you can drag and drop references onto a tag to associate them with that tag.

You can also manage tags when editing a reference in the Reference Editor.

References will often have pre-assigned tags, but you may also create and assign new ones. 

Full instructions:  https://knowledge.exlibrisgroup.com/RefWorks/Product_Documentation/RefWorks_User_Guide/0400_Managing_References#Organizing_References_by_Tags

To add personal notes to references:

Select a record from your library and click on the pencil icon in the reading pane to edit. 

Scroll down to "add more fields"

Select "personal note"

Include your notes in the new field