Uzun bir yolculuk insanı yorabilir.

• uzun = long
• bir = a / an
• yolculuk = journey, trip
• insanı = a person / a human being / one as the direct object
• yorabilir = can tire / may tire

So the sentence structure is basically subject + object + verb: Uzun bir yolculuk + insanı + yorabilir.

In normal Turkish, adjectives come before the noun, and bir usually sits between the adjective and the noun:

uzun bir yolculuk = a long journey

That is the standard, natural order.
bir uzun yolculuk is possible only in special, marked, or literary-style contexts, not as the usual everyday pattern.

Because insan is the direct object of the verb yorabilir. In this sentence, Turkish uses the accusative ending -ı, so:

insan → insanı

This gives the form insanı. The suffix is -ı because of vowel harmony.

That is a very common question. Yes, the accusative often points to a definite or specific object, but in Turkish there are also very common generic expressions like this one, where a singular noun can mean a person, one, or people in general.

So here insanı does not have to mean one particular person. It can mean something like:

• a person
• a human being
• one
• sometimes even people in general

This is a natural Turkish way to make a broad statement about human experience.

yorabilir comes from the verb yormak, which means to tire someone.

It can be broken down like this:

• yor- = verb stem
• -abil- = can / be able to
• -ir = a common present-aorist ending used for general statements

So yorabilir means can tire, may tire, or might tire, depending on context.
In this sentence, can tire is the most natural English match.

Because yormak and yorulmak are different:

• yormak = to tire someone / something out
• yorulmak = to get tired

In this sentence, the journey is causing tiredness, so Turkish uses yormak:

Uzun bir yolculuk insanı yorabilir.
A long journey can tire a person.

If you used yorulmak, the person would be the one becoming tired:

İnsan uzun bir yolculukta yorulabilir.
A person can get tired on a long journey.

Because the neutral word order in Turkish is usually Subject + Object + Verb.

Here that is:

• Uzun bir yolculuk = subject
• insanı = object
• yorabilir = verb

So the verb naturally comes last. Turkish can move parts around for emphasis, but verb-final order is the basic default.

You can, but the nuance changes a little.

• Uzun bir yolculuk sounds like a long journey, one instance of a long trip.
• Uzun yolculuk sounds more general or abstract, more like long travel or long journeying as a concept.

So Uzun bir yolculuk insanı yorabilir is often the more natural beginner-friendly form.

It is a general statement. Turkish often uses the singular for broad truths or general observations.

So even though yolculuk is singular, the meaning can still be general, like:

• A long journey can tire a person
• Long journeys can tire people

Turkish does this quite often.

Some natural alternatives are:

• Uzun yolculuklar insanı yorabilir.
  Long journeys can tire a person.

• Uzun bir yolculuk insanları yorabilir.
  A long journey can tire people.

• Uzun yolculuklar insanları yorabilir.
  Long journeys can tire people.

The original insanı is very common for a generic meaning, though, so the singular version is not strange at all.

This is about nuance.

• yorabilir = can tire / may tire
  This expresses possibility.

• yorar = tires / tends to tire
  This sounds more like a general fact or stronger statement.

So:

• Uzun bir yolculuk insanı yorabilir = A long journey can tire a person.
• Uzun bir yolculuk insanı yorar = A long journey tires a person / tends to tire a person.

The version with -abilir is a little softer and more cautious.