I bastoncini da trekking aiutano durante la discesa.

Because bastoncini is plural.

• il bastoncino = the trekking pole / the little stick
• i bastoncini = the trekking poles / the little sticks

In Italian, i is the masculine plural definite article used with many nouns that start with a consonant.

Also, I here is not the English pronoun I. It is pronounced like ee.

Bastoncini is the plural of bastoncino.

It comes from bastone = stick, pole, staff, with a diminutive ending, so historically bastoncino means something like small stick or little pole.

In real usage, though, bastoncini da trekking is simply the normal way to say trekking poles or hiking poles. You usually do not need to think about the diminutive every time.

Here da means something like for or used for.

So:

• bastoncini da trekking = trekking poles / poles for trekking

This is a very common Italian pattern:

• scarpe da tennis = tennis shoes
• occhiali da sole = sunglasses
• camera da letto = bedroom

So da + noun often shows purpose or function.

It is a loanword from English, but it is very commonly used in Italian.

In this phrase, trekking does not change form. It stays trekking, whether the whole noun phrase is singular or plural:

• il bastoncino da trekking
• i bastoncini da trekking

Because the subject is plural: i bastoncini da trekking.

The verb is aiutare = to help.
Present tense:

• aiuto = I help
• aiuti = you help
• aiuta = he/she/it helps
• aiutiamo = we help
• aiutate = you all help
• aiutano = they help

So i bastoncini da trekking aiutano means the trekking poles help.

Because Italian usually does not need subject pronouns when the verb ending already makes the subject clear.

So Italian normally says:

• aiutano = they help

rather than:

• loro aiutano

In your sentence, the noun phrase i bastoncini da trekking is already the subject, so adding loro would be unnecessary.

Yes. In Italian, aiutare can be used in a more general sense meaning to help, to be helpful, or to make things easier.

So:

• I bastoncini da trekking aiutano

can naturally mean:

• Trekking poles help
• Trekking poles are helpful

You do not always need to add a direct object.

Durante means during, and la discesa means the descent or the downhill part.

So durante la discesa means:

• during the descent
• when going downhill
• on the way down

In hiking context, discesa often refers to the downhill section of a route.

Italian uses articles more often than English.

So where English may say:

• during descent
• during the descent
• on descent

Italian very naturally says:

• durante la discesa

The article la does not always have to sound highly specific in English. It can be the normal Italian way to refer to that activity or phase.

Yes, but the nuance is a little different.

• durante la discesa = during the descent, focusing on the time/phase
• in discesa = while going downhill / on downhill terrain, often a bit more concise and situational

For example:

• I bastoncini da trekking aiutano durante la discesa.
• I bastoncini da trekking aiutano in discesa.

Both are possible. The original sentence sounds slightly more explicit.

Yes. Italian word order is fairly flexible.

The original order is very natural:

• I bastoncini da trekking aiutano durante la discesa.

But you could also say:

• Durante la discesa, i bastoncini da trekking aiutano.

That version puts more emphasis on during the descent.
The original sentence is the most neutral and straightforward.

A simple pronunciation guide is:

ee ba-ston-CHEE-nee da TREK-king a-yoo-TA-no doo-RAN-te la dee-SHEN-sa

A few useful points:

• i = ee
• ci in bastoncini sounds like chee
• aiu in aiutano sounds like a-yoo
• sc before e in discesa sounds like sh

So discesa sounds roughly like dee-SHAY-za or dee-SHEN-sa, depending on accent and how detailed you want to be in approximation.

It can work as a general statement.

Even though Italian uses la discesa, the sentence can still mean something general like:

• trekking poles are helpful when going downhill

So the article does not automatically force a very specific meaning such as one particular descent. Context decides that.