Это хорошее место для пикника.

Because место is a neuter singular noun, and the adjective has to agree with it.

• хороший = masculine
• хорошая = feminine
• хорошее = neuter
• хорошие = plural

So:

• хороший парк = a good park
• хорошая идея = a good idea
• хорошее место = a good place

In this sentence, место is neuter, so хорошее is the correct form.

In Russian, many nouns ending in -о or -е are neuter. Место ends in -о, so it is neuter.

That is why it goes with:

• хорошее место
• это место
• большое место (if that phrase makes sense in context)

As always, there are some exceptions in Russian, but место is a regular neuter noun.

Because the preposition для requires the genitive case.

The base form is:

• пикник = picnic

But after для, it changes to the genitive:

• для пикника = for a picnic / for picnics in the relevant sense

This is a very common pattern in Russian:

• для друга = for a friend
• для дома = for the house / for home
• для работы = for work
• для пикника = for a picnic

So the ending changes because of grammar, not because the word itself has a different basic meaning.

Это is very common in Russian and can mean things like:

• this
• it
• this is
• it is

In sentences like this one, это often works like this is or it is:

• Это хорошее место для пикника. = This is a good place for a picnic. / It’s a good place for a picnic.

Russian often uses это where English uses this or it, depending on context.

In present-tense Russian, the verb to be is usually omitted.

So English:

• This is a good place

becomes Russian:

• Это хорошее место

There is no separate word for is in normal present-tense sentences like this.

This is one of the most important differences between English and Russian. Russian often says, literally:

• This good place for a picnic

but the meaning is naturally understood as This is a good place for a picnic.

Yes. Russian word order is more flexible than English word order, although some versions sound more natural in certain contexts.

The most neutral version is:

• Это хорошее место для пикника.

But you might also hear:

• Для пикника это хорошее место.
• Хорошее это место для пикника. — possible, but more marked or expressive

Changing the word order often changes the focus or emphasis, not the core meaning.

For a learner, the original sentence is the best standard pattern to remember.

Usually for a picnic is the most natural translation here.

Russian does not always mark articles like English does, so пикника does not directly tell you a picnic versus the picnic in the way English articles do. The context usually decides that.

So:

• Это хорошее место для пикника. most naturally means This is a good place for a picnic.

In a broader context, it could also mean This is a good picnic spot.

A helpful stress guide is:

• Э́то хоро́шее ме́сто для пикника́

Approximate pronunciation:

• EH-ta kha-RO-shi-ye MYES-ta dlya peek-nee-KA

A few notes:

• Э́то = stress on the first syllable
• хоро́шее = stress on ро́
• ме́сто = stress on the first syllable
• пикника́ = stress on the last syllable
• для is often pronounced quickly, almost attached to the next word

The unstressed о sounds are reduced, so they may sound closer to a than to a clear English o.

Because it is the main predicate noun phrase of the sentence.

In Это хорошее место для пикника, the phrase хорошее место names what это is. In a present-tense sentence of identification like this, Russian typically uses the nominative:

• Это дом.
• Это моя сестра.
• Это хорошее место.

So:

• место = nominative singular
• хорошее agrees with место in nominative singular neuter

The only part here that changes case because of a preposition is пикника, because it follows для.

Yes, that is possible.

• Это хорошее место для пикника.
• Это место хорошее для пикника.

Both are understandable, but they are not exactly identical in emphasis.

• Это хорошее место для пикника sounds like the most neutral, standard statement.
• Это место хорошее для пикника puts a bit more focus on this place specifically.

In many situations, the first version is the one learners should use first.

No, it is a borrowing, ultimately from the same source as English picnic. Russian borrowed пикник, and it behaves like a normal masculine noun:

• пикник = nominative
• пикника = genitive
• пикнику = dative
• пикник = accusative
• пикником = instrumental
• пикнике = prepositional

So even though it is a borrowed word, its grammar fits regular Russian patterns quite well.