המדריך אומר שהמסלול על ההר לא קשה אם יש מספיק מים.

The prefix ה־ is the Hebrew definite article, meaning the.

So:

• מדריך = guide / instructor

• המדריך = the guide

• מסלול = route / trail / track

• המסלול = the trail

• הר = mountain
• ההר = the mountain

Unlike English, Hebrew usually attaches the directly to the noun as a prefix instead of writing it as a separate word.

Because ש־ is a very common attached word meaning that.

So:

• ש־ = that
• המסלול = the trail

Together:

• שהמסלול = that the trail

This is normal in Hebrew: short function words are often attached directly to the following word.

אומר is the masculine singular present-tense form of the verb לומר or להגיד type meaning to say.

Here it agrees with המדריך, which is masculine singular:

• המדריך אומר = the guide says / is saying

A useful point: Hebrew present tense often covers both:

• says
• is saying

So אומר can work for either, depending on context.

If the subject were feminine, you would get:

• המדריכה אומרת = the female guide says

In Hebrew, the verb to be is usually omitted in the present tense.

So Hebrew often says something like:

• המסלול לא קשה
  literally: the trail not difficult

But in natural English, that becomes:

• the trail is not difficult

This is called the zero copula in the present tense.

In past or future, Hebrew does use forms of to be, for example:

• המסלול היה קשה = the trail was difficult
• המסלול יהיה קשה = the trail will be difficult

קשה means difficult / hard.

It comes after the noun because Hebrew adjectives normally follow the noun they describe:

• מסלול קשה = a difficult trail

In this sentence it appears after לא:

• לא קשה = not difficult

Also, adjectives in Hebrew usually agree with the noun in gender and number.
Here, מסלול is masculine singular, so the adjective is understood as masculine singular too.

One interesting detail: in unvowelled Hebrew writing, the masculine singular and feminine singular of קשה are spelled the same, but they are pronounced differently:

• masculine: kashé
• feminine: kashá

Here, because מסלול is masculine, the pronunciation is kashé.

Literally, על ההר means on the mountain.

In this sentence, it describes the trail:

• המסלול על ההר = the trail on the mountain

Depending on context, English might also express this idea as:

• the mountain trail
• the trail up on the mountain

But the Hebrew wording is completely normal.

אם means if.

It introduces a condition:

• אם יש מספיק מים = if there is enough water

So the structure is:

• main statement: the trail on the mountain is not difficult
• condition: if there is enough water

Hebrew uses אם very much like English uses if.

יש is the standard Hebrew word for there is / there are or there exists / there exist.

So:

• יש מים = there is water / there are water supplies
• יש מספיק מים = there is enough water

A very important point for learners: יש does not change for singular or plural in the present tense.

So Hebrew says:

• יש ספר = there is a book
• יש ספרים = there are books

Same word: יש

Before a noun, מספיק often behaves like a fixed quantity word meaning enough or sufficient:

• מספיק מים = enough water
• מספיק זמן = enough time
• מספיק אנשים = enough people

In this use, מספיק usually stays in that basic form.

By contrast, when מספיק is used more like a regular adjective or predicate, it can agree:

• המשאבים מספיקים = the resources are sufficient

So in your sentence, מספיק מים is the normal way to say enough water.

מים is a great word to notice because it looks plural, and grammatically it often behaves like a plural word, but in meaning it corresponds to English water, which is usually treated as an uncountable noun.

For example:

• מים קרים = cold water
  literally, the adjective is plural: cold-plural

So yes, מים is grammatically plural in many ways.

But in translation, English normally just says water, not waters, unless the context is special.

It actually does have one here: ש־.

English can say either:

• The guide says the trail isn't difficult
• The guide says that the trail isn't difficult

Hebrew normally uses ש־ to introduce that kind of clause:

• המדריך אומר שהמסלול...

So ש־ is doing the job of English that.

In many everyday Hebrew sentences, this little prefix is extremely common after verbs like:

• אומר = says
• חושב = thinks
• יודע = knows
• מבין = understands

A simple pronunciation guide is:

ha-madrikh omer sheha-maslul al hahar lo kashe im yesh maspik mayim

A few helpful notes:

• המדריך = ha-madrikh
• אומר = omer
• שהמסלול = sheha-maslul
• ההר = hahar
• קשה = kashe
• יש = yesh
• מים = mayim

The stress is often near the end of Hebrew words, for example:

• ma-DRIKH
• o-MER
• mas-LUL
• ha-HAR
• ka-SHE
• mas-PIK

But MÁ-yim is stressed earlier than many learners expect.