If a singular noun already ends in 's', you don't need to add another 's'. You can just add an apostrophe at the end. Plural nouns refer to more than one person or thing, for example 'brothers'.
A preposition is a word that tells you where or when something is in relation to something else. Examples of prepositions include words like 'after', 'before', 'on', 'under', 'inside' and 'outside'.