Я домою чашки позже, а сейчас открою окно.

Домою means I’ll finish washing or I’ll wash the rest of.

It comes from the verb домыть / домывать, which is built from мыть (to wash) plus the prefix до-. That prefix often adds the idea of finishing something that is not fully done yet.

So Я домою чашки позже suggests something like:

• the cups are not fully dealt with yet, and
• the speaker will finish that job later.

This is slightly more specific than just saying I’ll wash the cups later.

Both are possible in some situations, but they are not identical.

• помою = I’ll wash
• домою = I’ll finish washing / wash up the remaining part

So домою implies completion of an already relevant task. It often sounds like:

• I’ve already started washing things, or
• some cups are still left, or
• the washing-up is an ongoing chore that I’ll complete later.

If the sentence were Я помою чашки позже, it would simply mean I’ll wash the cups later, without the extra sense of finishing the remaining washing.

Because both verbs are perfective:

• домыть → домою
• открыть → открою

In Russian, perfective verbs do not have a true present tense. Their present-looking forms are actually used for the future.

So:

• домою = I will finish washing
• открою = I will open

This is called the simple future of perfective verbs.

Because домыть is perfective.

A perfective verb describes an action as a whole completed event, and in Russian that kind of verb does not normally express a present ongoing action. So its non-past forms refer to the future.

Compare:

• домывать = imperfective → я домываю = I am finishing washing / I finish washing
• домыть = perfective → я домою = I will finish washing

The same pattern appears with:

• открывать → я открываю = I am opening / I open
• открыть → я открою = I will open

Чашки is the accusative plural of чашка (cup), because it is the direct object of домою.

For inanimate plural nouns, the accusative plural is the same as the nominative plural.

So:

• nominative plural: чашки
• accusative plural: чашки

That is why the form does not change.

Окно is also a direct object, so it is in the accusative case. But for inanimate neuter singular nouns, the accusative is the same as the nominative.

So:

• nominative singular: окно
• accusative singular: окно

That is why the form stays окно.

А often marks a contrast or a switch of focus.

Here the sentence means something like:

• I’ll finish the cups later, but right now I’ll open the window.

It contrasts later with right now, and also contrasts one action with another action.

Why not the others?

• и = just and, a simple addition
• но = but, often a stronger contradiction
• а = a natural contrast or change of topic: as for now / whereas / and meanwhile

In this sentence, а is the most natural connector.

In Russian, сейчас can mean not only now, at this exact moment, but also right now / in a moment / immediately.

So сейчас открою окно means:

• I’ll open the window right now
• I’m about to open the window

This is very natural Russian. The action is still in the future, but it is understood as immediate.

Both can often be translated as later, but they are not always identical.

• позже = later, often in contrast to now
• потом = afterward / then / later

In this sentence, позже fits especially well because the speaker contrasts:

• позже = later
• сейчас = now

So the pair позже ... сейчас ... sounds very natural.

Открою is perfective because opening the window is seen as a single complete action: the speaker will do it and it will be done.

That is exactly the kind of situation where Russian prefers the perfective.

An imperfective option like буду открывать окно would usually sound strange here, because it focuses on the process of opening rather than the simple fact that the window will be opened.

So:

• сейчас открою окно = natural, I’ll open the window right now
• сейчас буду открывать окно = unusual here, more like I’m going to be in the process of opening the window

Not always.

Russian often drops subject pronouns when the verb ending already shows who is doing the action.

So these are both possible:

• Я домою чашки позже, а сейчас открою окно.
• Домою чашки позже, а сейчас открою окно.

Including Я can make the subject a little more explicit. It may sound:

• clearer,
• slightly more personal,
• or mildly emphatic.

But in ordinary conversation, Russian often omits it.

Yes, Russian word order is flexible.

The given version is very natural:

• Я домою чашки позже, а сейчас открою окно.

It presents the first action, then contrasts it with the immediate action.

Other word orders are also possible, for example:

• Сейчас открою окно, а чашки домою позже.

This puts more emphasis on what I’m doing right now first.

Russian word order often reflects focus, contrast, and what the speaker wants to highlight, rather than strict grammatical necessity.

The dictionary forms are:

• домыть or домывать for the washing idea
• открыть or открывать for the opening idea

More exactly:

• домою is from домыть (perfective)
• открою is from открыть (perfective)

And their imperfective partners are:

• домывать
• открывать

This perfective–imperfective pairing is very important in Russian.

Usually it means the cups in question—the cups relevant in the situation.

Because of the verb домою, there is often an implication that these are the cups that still need attention, so in context it may feel like:

• I’ll finish the cups later
• I’ll finish washing the remaining cups later

Whether it means literally all cups or just the cups under discussion depends on context, but the sentence definitely suggests a specific set of cups, not cups in general.