Conjugation is the change that takes place in a verb to express tense, mood, person, etc. The term is commonly used for verbs which in many languages can be classified according to the shape of the affixes endings they may take to indicate different things.
An example in English shows how the verb break is conjugated:
Present Simple
I, You, We, They: break
He, She, It: breaks
Present Continuous (Progressive)
I: am breaking
You, We, They: are breaking
He, She, It: is breaking
Present Perfect
I, You, We, They: have broken
He, She, It: has broken
Past Simple
I, You, We, They, He, She, It: broke
Past Continuous
I, He, She, It: was breaking
You, We, They: were breaking
Past Perfect
I, You, We, They, He, She, It: had broken
Conjugation can indicate person, number, tense, aspect, mood, voice or other grammatical information, often represented morphologically on the verb.