Both Tags and Notes are an easy, on-the-fly way for you to categorize a title or jot down a thought as you discover titles of interest in Edelweiss+.
Tags are labels or keywords that you can attach to titles for quick filtering and grouping purposes. "August Release," "Own-Voices Title," "Local Author," etc. Anytime you have wanted to create a list of like titles, Tags were the answer.
The Notes option is where you can attach your own notes to a title. This gives you an area to write something specific about a title and in greater detail than a Tag.
The main difference between a Tag and a Note is that a Note simply lives with the title and cannot be searched for or filtered for. A best practice is often to Tag a title so you can find it later and write a more extensive note in the Notes field.