MORPHOLOGY

A speaker of a language also knows how words are structured. The term word can be used in different senses. On the one hand, vocabulary items, i.e. entries in the dictionary (e.g. take), are called words, but on the other hand the different inflected forms of a word

*take

*takes

*taking

*took

*taken 

>>> are also called words.

So, the question is what is Morphology ?

Simple answer, Morphology is the study of the minimal meaningful units of language.  
Words have internal structure consisting of smaller units called Morpheme. 
  Morphology studies the structure of words, however from a semantic viewpoint rather than from the viewpoint of sound. It is intimately related to syntax. For everything that is larger than a word is the domain of syntax. Thus within morphology one considers the structure of words only, and everything else is left to syntax. The first to notice is that words come in different classes. 

For example :
verbs (/to imagine/)
nouns (/a car/),
 adverbs (/slowly/)
adjectives (/red/). 

It also inlude suffix and preffix (e,g, unlike, agreement). 

For Verbs take the endings /s/, /ed/, and /ing/ but we have to know there is clasificaton namely : regular and irregular verb (e.g. took, taken), nouns only take the ending /s/. Adjectives and adverbs on the other hand do not change (They can be distinguished by other criteria).

Ex :

I take it

He takes it

He is taking it

I took it

Refferences : Charles F. Mayer, Inroduction to Linguistics, 2009 [pdf]

Marcus Kracht, Inroduction to Linguistics [pdf]

Companion to English Linguistics [pdf]