It is understood that, usually, the preposition is `placed` `before` a noun in a sentence. Since a noun comes at the beginning or end of a sentence a preposition can also come in these two positions. Prepositions help to relate the subject and the object of a sentence.
We have to remember that a group of words can also function as a noun. This group of words, or phrase, usually has a noun which is modified by an adjective which is preceded by an article. This group is called a noun phrase.
The cat sat on the old, brown carpet.
Into the solemn, silent assembly he walked.
[The words in bold are prepositions and the nouns are preceded by adjectives which are preceded by articles. The preposition comes before the article].
Many prepositions are single syllable words like, at, on, up, down, in, through, over, etc. Many others have two syllables like, behind, below, above, along, across, etc. Still others are phrases like, in accordance with, with respect to, etc.
To find a preposition look for a name [noun] of either someone or something. Or find one of the articles [a, an & the] or identify an adjective, and look at the word before. This will probably be a preposition. [Here, in this paragraph too, the words in bold are prepositions and the nouns are preceded by adjectives and articles. The preposition comes before the article].
Imagine a table with a box on it. Then we can make the following statements to illustrate the use of some prepositions.
1] He put a ball into the box, i.e. this shows movement from outside to inside the box. 2] There is a ball in the box. This does not show movement. 3] There is a ball on the table, i.e. on the surface of the table. 4] He put a ball onto the table, i.e. from elsewhere onto the surface of the table. This preposition [ onto] also shows movement. 5] If we walk lengthwise of a road or a river bank we walk along this road, etc. 6] But, if we go breadth wise we go across it. 7] If there is a heavy object then it can go through the bottom of a cardboard box . 8] We ascend or go up the stairs, and we descend or go down them. 9] If a ball is placed close to a box but not touching it, then the ball is next to or beside [ by the side of] the box. 9] But, if we place it farther away, but not too far away, then the ball is near the box. 10] Similarly, we can use synonyms to say that The ball is over/ above or under/ below a table. Will this help understand some prepositions?