-For a dictionary you would use it when you come across a word while reading books, magazines, or an article on your phone if you see a word you cannot pronounce or do not understand.
-If your using a thesaurus then you should use it to find synonyms for any word except slang as far as I know. A thesaurus can help you find words similar in meaning to JOY which would be: Happy, Joyful, Cheerful etc.
- A glossary is for when your reading a book and you don't understand some words. You open the book then proceed to the back of the book where you will find a lot of words with definitions a lot like dictionaries.
Glad to help! :)
