Nouns, main verbs, adjectives and adverbs are usually content words. Auxiliary verbs, pronouns, articles, and prepositions are usually grammatical words.
Example
‘We flew over the mountains at dawn'.
In the classroom
There is an important difference in pronunciation between content and grammatical words. Content words tend to be stressed and grammatical words are often pronounced in a reduced form or with a schwa sound. Practice of this can be provided in listening comprehension activities that require learners to reconstruct what they have heard.
Further links:
https://www.teachingenglish.org.uk/article/dictation-3-texts