Prepositions

Prepositions are words that link a noun or a pronoun to another word in the sentence.

Here is a list of some of the most common prepositions: about, between, above, beyond, across, but, after, by, against, despite, along, down, amid, during, around, except, as, for, at, from, before, in, behind, inside, below, into, beneath, like, beside, near, of, since, off, through, on, toward, onto, under, opposite, underneath, out, until, outside, upon, over, with, past, within
A noun always follows a preposition. A prepositional phrase is a preposition and its object. A prepositional phrase can be two or three words long, as these examples show: on the roof, in the door, under the bed.
However, prepositional phrases can be much longer, depending on the length of the preposition and number of words that describe the object of the preposition. 

• There is a cat on the roof.
• He is fond of children.
• She sat by the fire.
• The lion and the unicorn fought for the crown.

Most English prepositions have several different functions. At the same time, different prepositions can have very similar uses.
When we use verbs after prepositions, we use -ing forms, not infinitives.

• We are thinking of visiting them. (NOT We are thinking of to visit them.)
• He insisted on being paid at once. (NOT He insisted on to be paid at once.)
• I hate the idea of getting old.
• I am not very good at cooking.

When to is a preposition, it is followed by an -ing form.

• I look forward to seeing you soon.
• She objected to my entering her room.