Первого мая мы собираемся поехать за город и устроить пикник.

Because in Russian, dates are usually expressed with the day in the genitive plus the month in the genitive.

So Первого мая means on the first of May / on May 1st.

• первое мая would be incorrect in this sentence
• первого is the genitive form of первое
• мая is the genitive form of май

This is the normal pattern for dates:

• первого января — on January 1st
• второго февраля — on February 2nd
• девятого марта — on March 9th

Because after an ordinal number used in a date, the month goes in the genitive.

So:

• первое мая is not the standard date form
• первого мая is the correct date expression

Think of it as a fixed pattern:

• первого мая
• двадцать пятого декабря
• третьего июля

Russian uses this structure where English uses on May 1st.

In a way, yes. English needs on for dates, but Russian often does not.

So Первого мая мы собираемся... directly means On May 1st, we are planning...

Russian can also use в in some date expressions, but with a full date like this, the genitive form by itself is very common and natural.

Here собираемся means are planning, intend, or are going to.

The verb is собираться, which can mean different things depending on context:

• to get ready
• to intend / plan
• sometimes literally to gather

In this sentence, it clearly means we are planning/intending.

So:

• мы собираемся поехать = we are planning to go
• мы собираемся устроить пикник = we are planning to have/organize a picnic

It does not mean that the people are physically gathering together in this sentence.

Because Russian often uses the present tense of собираться to talk about a future intention or plan.

So мы собираемся поехать literally looks like we are getting ready / we are planning to go, but in natural English it often becomes we are going to go or we plan to go.

This is similar to English We are going to leave tomorrow: grammatically present, but referring to the future.

Because поехать is the perfective verb, and it fits a planned, one-time trip very well.

Compare:

• ехать — imperfective, focuses on the process of going, ongoing movement, or repeated/habitual action
• поехать — perfective, focuses on setting off / making the trip as a whole

In this sentence, the idea is a specific planned outing, so поехать is natural:

• мы собираемся поехать за город = we plan to go out of town

If you used ехать, it would sound less natural here unless you wanted a different nuance.

For the same general reason: устроить is perfective, so it presents the picnic as a single completed event.

Compare:

• устраивать — imperfective, to organize/arrange in general, repeatedly, or as a process
• устроить — perfective, to organize/set up once, successfully

Here the sentence means they plan to have one picnic on that occasion, so устроить пикник is the natural choice.

За город literally means beyond the city, but idiomatically it means:

• out of town
• to the countryside
• outside the city

It is a very common Russian expression.

So:

• поехать за город = to go out of town / to go to the countryside

It does not necessarily mean very far away; it just means leaving the city area.

Because за here expresses movement to a place beyond something.

With motion, за can take the accusative case:

• за город — to beyond the city, i.e. out of town

Compare:

• в город — into the city
• из города — out of the city, from the city
• за город — beyond the city, outside the city

So the choice of preposition changes the meaning quite a lot.

Because город here is in the accusative singular, and for masculine inanimate nouns, the accusative often looks exactly like the nominative.

So:

• nominative: город
• accusative: город

That is why the form does not visibly change.

If it were a noun with a different accusative ending, the change would be easier to see.

Because one verb of intention can govern multiple infinitives joined by и.

So the structure is:

• мы собираемся — we plan
• поехать за город — to go out of town
• и устроить пикник — and have/organize a picnic

This is completely normal in Russian, just like in English:

• We plan to go out of town and have a picnic

Russian does not need to repeat собираемся before the second infinitive.

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

• устроить что? — пикник

But пикник is a masculine inanimate noun, so its accusative singular looks the same as the nominative:

• nominative: пикник
• accusative: пикник

So the case is accusative, even though the form does not change.

Yes. Russian word order is fairly flexible, and changes usually affect emphasis, not basic meaning.

Original:

• Первого мая мы собираемся поехать за город и устроить пикник.

Other possible orders:

• Мы собираемся первого мая поехать за город и устроить пикник.
• Мы первого мая собираемся поехать за город и устроить пикник.

The original puts Первого мая first, which gives the date some emphasis, like:

• As for May 1st, we’re planning to go out of town and have a picnic

Because Russian has no articles like a, an, or the.

So:

• за город can mean out of town / outside the city
• устроить пикник can mean have a picnic or organize the picnic, depending on context

Russian leaves that kind of definiteness to context rather than using articles.