Definition- A preposition is a word placed before a noun, pronoun or noun phrase to show the relation between the person or thing denoted by it and something else mentioned in the sentence.
For example-
1-My books are in my bag.( relation between my bag and books)
2- The man jumped into ??????the river.(relation between the river and jumping)
Rules for prepositions-
A preposition needs an object and this object can be a noun , pronoun, gerund,noun phrase or clause.
* In spring (noun)
* Tired of waiting(gerund)
* For me(pronoun)
* He is afraid of what his teachers might say (noun clause).
Sometimes this object may be an adverb of time or place or an adverb phrase.
* I haven't seen him since then.(then - adverb of time)
* From here,my school is 5 minutes drive.(here - adverb of place)
* Somebody called me from across the road.(across the road - adv.phrase).
Kinds of Prepositions--
There are four kinds of preposition:
1-Simple prepositions: at,by,in, from,on,to etc.
2- Compound prepositions: beside, across, inside, within etc.
3-Prepositional phrases: in front of, in case of, in spite of ,by virtue of etc.
4- Participial prepositions: regarding, concerning etc.