Sentences are constructed by abiding to two main rules: every sentence contains a subject and predicate, and the subject always precedes the predicate. The subject consists of the main noun partaking the action of the sentence and the predicate contains the verb or action partook.
The simplest sentence in the English language needs to only contain a noun and a verb. The sentence "Mary walks." contains a subject, "Mary," and a predicate, "walks." Most sentences, however, contain other word types such as adjectives, adverbs, prepositions and conjunctions.
Adjectives are used to describe nouns and generally precede the noun. Adverbs can describe verbs, adjectives, or even other adverbs. Order in a sentence can vary, but generally adverbs follow the word they are describing. The predicate of a sentence can sometimes contain an object noun. While the subject is the noun performing the action, the object is the noun being acted upon. In the sentence "Mary walks on a road," "Mary" is the subject noun and "road" is the object noun.
Two other key aspects of a sentence are prepositions and conjunctions. Prepositions signify location and generally connect a verb with an object noun. In the sentence, "Mary walks on a road," "on" is the preposition. Conjunctions are simple connecting words, such as "and" and "but," used to join two parts of a sentence.