Завтра я сдам сочинение по литературе, если сегодня вечером допишу последний абзац.

Сдам is the 1st person singular future form of сдать.

In this sentence, сдать сочинение means to hand in / submit an essay.

So:

• я сдам = I will hand in
• not I will write

This verb is about turning something in, for example to a teacher.

Because сдать is a perfective verb.

In Russian:

• imperfective verbs usually make the future with буду + infinitive
• perfective verbs make the future with a single form

So:

• сдавать → буду сдавать = will be handing in / will hand in (process, repeated action, or less focus on completion)
• сдать → сдам = will hand in, with emphasis on completion

Here the speaker means a single completed result: tomorrow the essay will be submitted.

These verbs are related but not identical:

• пишу = I am writing / I write
• напишу = I will write / I will finish writing
• допишу = I will finish writing the rest / complete what I haven’t finished yet

The prefix до- often adds the idea of finishing something that has already been started.

So допишу последний абзац means:

I finish writing the last paragraph
or more naturally,
I finish off the last paragraph

This suggests the essay is already mostly done.

That is a very common question.

In Russian, when the condition is about the future, Russian normally uses a future form after если.

So Russian says:

• если сегодня вечером допишу... = if I finish tonight...

Even though English usually uses the present tense after if, Russian does not follow that rule here.

So this is normal Russian grammar, not a special exception.

Because it is understood from the verb form.

• допишу already means I will finish writing
• the ending -у tells you the subject is I

Russian often omits subject pronouns when they are clear from context or verb endings.

So:

• если сегодня вечером я допишу... = possible
• если сегодня вечером допишу... = also natural, and often smoother

Both are correct. The version without я sounds a bit less repetitive.

Сочинение means essay or composition, especially in a school context.

По литературе means for literature / in literature / on the subject of literature.

So сочинение по литературе is best understood as:

• a literature essay
• an essay for literature class

The preposition по is often used with school subjects:

• по математике = in math / for math
• по истории = in history / for history
• по литературе = in literature / for literature

Because the preposition по here requires the dative case.

The noun литература changes like this:

• nominative: литература
• dative: литературе

So:

• по литературе = for literature / in literature

This is a very useful pattern to remember with school subjects.

It is the accusative case, because it is the direct object of допишу.

The speaker will finish writing what?
→ последний абзац

For masculine inanimate nouns, the accusative often looks exactly like the nominative:

• nominative: последний абзац
• accusative: последний абзац

So the form does not change, even though the case function does.

Because вечером can function as a time expression by itself and often means in the evening / tonight.

This is a common Russian pattern:

• утром = in the morning
• днём = during the day / in the daytime
• вечером = in the evening
• ночью = at night

Historically, this is connected with the instrumental case, but for learners it is often easiest to memorize these as standard adverbial time forms.

So:

• сегодня вечером = this evening / tonight

You do not need в here.

Because если сегодня вечером допишу последний абзац is a subordinate clause.

Russian normally separates subordinate clauses with a comma, including clauses introduced by:

• если = if
• когда = when
• потому что = because
• что = that

So the comma here is required.

Yes. Russian word order is flexible, and changing it can shift emphasis.

The given sentence:

Завтра я сдам сочинение по литературе, если сегодня вечером допишу последний абзац.

This is a neutral, natural order.

Possible variations include:

• Если сегодня вечером допишу последний абзац, завтра сдам сочинение по литературе.
• Сочинение по литературе я сдам завтра, если сегодня вечером допишу последний абзац.

These all mean roughly the same thing, but the focus changes:

• starting with если... emphasizes the condition
• starting with сочинение по литературе... emphasizes what will be handed in
• starting with завтра emphasizes the time

Together they make the sentence feel very goal-oriented and result-focused.

• допишу = I will finish writing the last paragraph
• сдам = I will hand in the essay

Both are perfective, so both point to completed actions, not ongoing processes.

The sentence is about a chain of completed results:

1. finish the last paragraph tonight
2. hand in the essay tomorrow

That is why the sentence sounds decisive and practical.

It could, but the meaning would change.

For example:

• если сегодня вечером буду дописывать... would mean something more like if I’m going to be finishing/writing more tonight, which sounds less complete and less natural here.
• завтра буду сдавать сочинение could suggest the process or occasion of handing it in, not simply the completed result.

In this sentence, the speaker cares about whether the essay gets finished and submitted, so perfective verbs are the best choice.

Not always exactly, but essay is the best translation here.

Сочинение can mean:

• a school essay
• a composition
• sometimes a written piece on a set topic

In this sentence, because of по литературе, it clearly means a school essay for literature class.