Без помощи трудно добиться результата.

Because без always requires the genitive case in Russian.

• Dictionary form: помощь = help
• After без: без помощи = without help

So this is not a different word, just the correct case form after the preposition без.

Because the verb добиться takes its object in the genitive, not the accusative.

So:

• добиться результата = to achieve a result
• not добиться результат

This is just something you need to learn with the verb. A very common pattern is:

• добиться успеха = achieve success
• добиться цели = achieve a goal
• добиться результата = achieve a result

Добиться means to achieve, to attain, or to get through effort.

It often suggests that the result was not easy and required work, persistence, or struggle. So it is a little stronger than simply get.

Its imperfective partner is добиваться.

• добиваться результата = to be trying to achieve a result
• добиться результата = to achieve a result, to succeed in getting it

In your sentence, the infinitive is добиться, the perfective form, because the sentence speaks about reaching a completed result.

Russian often uses impersonal constructions where English uses it.

In English, we say:

• It is difficult to achieve a result without help.

In Russian, you can simply say:

• Трудно добиться результата.

There is no need to add a subject. The word трудно already creates the meaning it is difficult.

So the sentence is literally closer to:

• Without help, difficult to achieve a result.

But in natural English, you translate it with it.

Because трудно here is not an adjective modifying a noun. It is a predicative word/adverb-like form meaning it is difficult.

Compare:

• трудная задача = a difficult task
• трудный вопрос = a difficult question
• трудно понять = it is difficult to understand

So in your sentence, трудно describes the whole action добиться результата, not a noun.

Because Russian commonly uses the pattern:

• трудно + infinitive = it is difficult to do something

So:

• трудно добиться = it is difficult to achieve
• трудно понять = it is difficult to understand
• трудно сказать = it is difficult to say

The infinitive names the action in a general way, just like English to achieve in it is difficult to achieve.

Yes. Russian word order is fairly flexible.

Your sentence:

• Без помощи трудно добиться результата.

Another natural version:

• Трудно добиться результата без помощи.

Both mean essentially the same thing. The difference is mainly emphasis:

• Без помощи at the beginning emphasizes the condition without help
• placing it at the end sounds a little more neutral in some contexts

So the original sentence is perfectly natural, especially if the speaker wants to stress the lack of help.

Russian has no articles like a and the.

So результата by itself does not tell you whether English should use:

• a result
• the result
• sometimes even just results in another context

You choose the English article from context. In this sentence, a result is the most natural general translation:

• Without help, it is difficult to achieve a result.

Depending on context, it could also mean:

• Without help, it is difficult to achieve the result.

But that would usually need a specific context in English.

It is a very natural and common way, but not the only one.

Possible alternatives include:

• без помощи = without help
• без посторонней помощи = without outside help
• самостоятельно = independently, on one’s own

The exact choice depends on nuance.
For example:

• Без помощи трудно добиться результата. = Without help, it is hard to achieve a result.
• Самостоятельно трудно добиться результата. = It is hard to achieve a result on your own.

So без помощи is a good general phrase.

Yes, it is natural.

A native speaker could also say:

• Без помощи сложно добиться результата.
• Трудно добиться результата без помощи.
• Без посторонней помощи трудно добиться результата.

The difference between трудно and сложно is small here:

• трудно = difficult, hard
• сложно = difficult, complicated

In many everyday contexts, both work well. Your original sentence sounds normal and idiomatic.