Der Lernstoff für die Klausur ist schwer, aber mit einer guten Lernstrategie ist er machbar.

The noun Lernstoff is masculine, so it takes der in the nominative singular.

A very useful rule for German compound nouns is:

• the last part decides the gender

Here, the last part is Stoff, which is masculine: der Stoff.
So the full compound is also masculine: der Lernstoff.

This is why later the sentence uses er to refer back to it.

Lernstoff means the material or content that has to be learned, especially for school or university.

It often refers to:

• the subject matter
• the syllabus content
• the material covered for a test

It is a very common academic word in German. In English, depending on context, you might translate it as:

• material
• course material
• content to study
• stuff you need to learn

Because für always takes the accusative case.

So:

• die Klausur is feminine singular
• feminine singular in the accusative is still die

That is why you get:

• für die Klausur

If the noun were masculine, you would see the article change:

• für den Test

So this is a classic case rule:

• für + accusative

Both can mean a test or exam, but they are not always identical.

• Klausur often means a written exam, especially in school or university
• Prüfung is a broader word meaning exam/test in general
• Examen is often used for major formal exams

So in this sentence, Klausur suggests a specific academic test, often written.

Because mit always takes the dative case.

The noun Lernstrategie is feminine, so in the dative singular:

• eine becomes einer

And the adjective ending also changes:

• gut becomes guten

So:

• nominative: eine gute Lernstrategie
• dative after mit: mit einer guten Lernstrategie

This is another very important case rule:

• mit + dative

Because German keeps the finite verb in second position in a main clause.

The second clause begins with:

• mit einer guten Lernstrategie

That whole phrase takes the first position. So the verb must come next:

• Mit einer guten Lernstrategie ist er machbar.

After that comes the subject:

• er

So the structure is:

• [first element] + [verb] + [subject] + ...

You could also say:

• ..., aber er ist mit einer guten Lernstrategie machbar.

That is also grammatical, but it puts the emphasis in a slightly different place. The original sentence emphasizes with a good learning strategy.

Er refers back to der Lernstoff.

Since Lernstoff is masculine, the matching pronoun is:

• er = he/it

In English, we usually say it, but German noun gender controls the pronoun.

So:

• Der Lernstoff ... er

German usually needs an explicit subject, so you normally do not leave er out here.

Yes, in this sentence schwer and schwierig are both possible.

• schwer can mean heavy, but also difficult
• schwierig means difficult more specifically

So:

• Der Lernstoff ist schwer.
• Der Lernstoff ist schwierig.

Both work.

The version with schwer sounds very natural. German often uses schwer in exactly this kind of context.

Machbar means:

• doable
• manageable
• possible to accomplish

It comes from:

• machen = to do, make
• -bar = a suffix meaning something like -able

So machbar literally means doable.

This suffix is very useful in German. Other examples:

• essbar = edible
• sichtbar = visible
• lösbar = solvable

So machbar is a good word to learn as part of a bigger pattern.

Because the sentence joins two main clauses:

• Der Lernstoff für die Klausur ist schwer
• aber mit einer guten Lernstrategie ist er machbar

In German, main clauses linked by conjunctions like aber are usually separated by a comma.

So the comma here is standard and necessary.

Because schwer and guten are doing different jobs.

In:

• Der Lernstoff ... ist schwer

schwer is a predicate adjective. It comes after ist, so it does not take an adjective ending.

But in:

• mit einer guten Lernstrategie

guten comes before a noun and directly describes it, so it is an attributive adjective. Attributive adjectives do take endings in German.

So compare:

• Der Lernstoff ist schwer. → no ending
• eine gute Lernstrategie → adjective ending needed

This difference is very important in German adjective grammar.

Yes. German often allows several natural versions. For example:

• Der Lernstoff für die Klausur ist schwer, aber mit einer guten Lernstrategie kann man ihn schaffen.
• Der Lernstoff für die Klausur ist schwer, aber er ist mit einer guten Lernstrategie gut zu bewältigen.

The original sentence is nice because it is clear and compact.
Using machbar makes it sound encouraging: the material is hard, but still doable.