Prepositions are linking or connecting words. They link words that follow them to other words in a sentence. We can equally say a preposition is a connecting word which shows the relationship of a noun or pronoun to another word in a sentence. Examples:
What are tenses?
The Simple Present
The Present Continuous/Progressive
The Present Perfect Tense
The Present Perfect Continuous
The Simple Past Tense, The Past Continuous Tense
The Past Perfect Tense
The Past Perfect Continuous Tense
Simple Future Tense, The Future Perfect Tenses
Future Continuous, Subject/Verb Agreement
What are verbs?
Forms of Verbs
The Passive and Active Voices