what is a preposition?
A preposition is a part of speech that shows the relationship between a noun or pronoun and other words in a sentence. It is used to indicate location, time, direction, manner, and other similar relationships. To understand what a preposition is, you can follow these steps:
1. Look for words that express relationships: Prepositions typically show relationships between other words in a sentence. Common prepositions include "in," "on," "at," "by," "over," "under," "between," and "through," among others.
2. Identify the object of the preposition: After finding the preposition, look at the word or phrase that follows it. This word or phrase is called the object of the preposition. In the sentence, "She walked in the park," the preposition "in" shows the relationship between the verb "walked" and the object "the park."
3. Determine the relationship expressed: Once you have identified the preposition and its object, consider the relationship being expressed. For example, the preposition "in" in the sentence "She lives in New York" indicates location.
Understanding prepositions is essential for constructing grammatically correct sentences and conveying precise meanings.
You can find the definition here.
http://dictionary.reference.com/browse/preposition
However, I've always had difficulty understanding that definition. The best way to learn prepositions is to memorize the common ones.
http://grammar.ccc.commnet.edu/grammar/preposition_list.htm
Also, I recommend you learn to recognize prepositional phrases.
http://grammar.uoregon.edu/phrases/prepositionalP.html