A sentence is made up of words put together to do a certain job. Words are the smallest meaningful units of a sentence.
barks / dog / angry
Each of the above words work differently in a sentence:
Words are linked to create a phrase to build up the sentence.
A phrase is used in place of a word to give more information about it. A noun phrase is built around a noun, making the noun the head word of a noun phrase.
The angry dog.
In this noun phrase, the noun ‘dog’ is the head word.
A phrase that comes immediately before a verb is the verb’s subject. A phrase that follows a verb is the verb’s object.
Phrases are linked to a main verb to make a clause.
A clause is one or more phrases linked to a verb that work very tightly together.
The angry dog barks.
In this clause - which could also be used as a sentence - the noun phrase is 'the angry dog' and the verb is 'barks'. The head word of the noun phrase is the noun ‘dog’.