Theory:

Anaphora is one of the most commonly used rhetorical device. It is a type of repetition where a word or phrase is repeated at the beginning of a phrase, sentences, stanza, or a paragraph. It is also known as Repetitio.
Pronunciation Guide
Anaphora-- Ana (as in analyse) -- pho (as in phone) -- ra (as in Dora)
Let us consider the poem "Your Space" by David Bates as an example.
Example:
Speak gently! – It is better far
     To rule by love, than fear
Speak gently – let not harsh words mar
     The good we might do here!
 
Speak gently! – Love doth whisper low
     The vows that true hearts bind;
And gently Friendship’s accents flow;
     Affection’s voice is kind.
 
Speak gently to the little child!
     Its love be sure to gain;
Teach it in accents soft and mild:-
     It may not long remain.
 
Speak gently to the young, for they
     Will have enough to bear –
Pass through this life as best they may,
     ‘T is full of anxious care!

Speak gently to the aged one,
      Grieve not the care-worn heart;
The sands of life are nearly run,
      Let such in peace depart!
 
Speak gently, kindly, to the poor;
      Let no harsh tone be heard;
They have enough they must endure,
     Without an unkind word!
 
Speak gently to the erring – know,
     They may have toiled in vain;
Perchance unkindness made them so;
     Oh, win them back again!
 
Speak gently! – He who gave his life
     To bend man’s stubborn will,
When elements were in fierce strife,
     Said to them, ‘Peace, be still.’
 
Speak gently! – ’tis a little thing
     Dropped in the heart’s deep well;
The good, the joy, which it may bring,
     Eternity shall tell.
The above poem is an example of anaphora because the phrase "speak gently" gets repeated at the beginning of each stanza.
 
The following example is an extract from a popular speech by Martin Luther King, Jr. The speech is known as "I have a Dream". It got its name from the anaphora "I have a dream". Interestingly, the popularity of speech can also be because of the repetition of the phrase.
Example:
I say to you today, my friends, so even though we face the difficulties of today and tomorrow, I still have a dream. It is a dream deeply rooted in the American dream.
I have a dream that one day this nation will rise up and live out the true meaning of its creed: "We hold these truths to be self-evident; that all men are created equal."
I have a dream that one day on the red hills of Georgia the sons of former slaves and the sons of former slave owners will be able to sit down together at the table of brotherhood.
I have a dream that one day even the state of Mississippi, a state sweltering with the heat of injustice, sweltering with the heat of oppression, will be transformed into an oasis of freedom and justice.
I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character.
Example of anaphora from the poem "Wind":
Wind, come softly.
Don’t break the shutters of the windows.
Don’t scatter the papers.
Don’t throw down the books on the shelf.
There, look what you did — you threw them all down.
You tore the pages of the books.
You brought rain again.

You’re very clever at poking fun at weaklings.
Frail crumbling houses, crumbling doors, crumbling rafters,
crumbling wood, crumbling bodies, crumbling lives,
crumbling hearts —
the wind god winnows and crushes them all.

He won’t do what you tell him.
So, come, let’s build strong homes,
Let’s joint the doors firmly.
Practise to firm the body.
Make the heart steadfast.
Do this, and the wind will be friends with us.

The wind blows out weak fires.
He makes strong fires roar and flourish.
His friendship is good.
We praise him every day.
In this poem, the words "Don't" and "You"(highlighted in green) were used at the beginning of almost every new sentence in Stanza 1 and 2.
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-6. The Crocodile - Lewis Carroll (pp. 99-100). Published by the Tamil Nadu Textbook and Educational Services Corporation.
 
State Council of Educational Research and Training (2019). Term-1 English Standard-7. Your Space by David Bates (pp. 70-72). Published by the Tamil Nadu Textbook and Educational Services Corporation.
 
https://www.history.com/topics/civil-rights-movement/i-have-a-dream-speech
 
National Council of Educational Research and Training (2006). Beehive. Wind - A.K.Ramanujan (pp. 30-31). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.