Guru menjelaskan bahwa kampanye yang baik harus praktis dan mudah dipahami.

Bahwa is a conjunction that introduces a "that-clause", like “that” in English:

• Guru menjelaskan bahwa … = The teacher explained that …

In spoken Indonesian, bahwa is often omitted:

• Guru menjelaskan (bahwa) kampanye yang baik harus praktis dan mudah dipahami.

Both versions are correct. Using bahwa sounds a bit more formal and clear, especially in writing.

Indonesian does not have articles like “a/an” or “the”. The nouns:

• guru can mean “a teacher” or “the teacher”
• kampanye can mean “a campaign” or “the campaign”

Context decides whether it’s specific or general.
If you really want to show “a teacher”, you can say seorang guru (one person, a teacher), but it’s not required here.

Yang introduces a descriptive (relative) clause. Literally:

• kampanye yang baik = a campaign *that is good*

You can say kampanye baik, and it’s still correct. The nuance:

• kampanye baik – simple noun + adjective, “good campaigns” in general.
• kampanye yang baik – slightly more emphatic/defining: “campaigns that are good (as opposed to bad ones)”.

In many contexts they are interchangeable; yang is very common when you want to define or highlight the quality.

In Indonesian, adjectives normally come after the noun:

• kampanye baik = good campaign
• guru pintar = smart teacher
• rumah besar = big house

So kampanye yang baik follows the usual pattern: noun + (yang) + adjective.
Putting the adjective before the noun, like baik kampanye, is not standard.

The root word is jelas = “clear”.
menjelaskan is built as:

• jelas (clear)
• meN- + jelas + -kan → menjelaskan = “to explain (to make something clear)”

So menjelaskan means “to explain something”.
There is no verb menjelas; you need the full form menjelaskan.

Compared with other verbs:

• mengatakan = to say, to state
• menerangkan = to explain (similar to menjelaskan, but menjelaskan is more common in standard/formal contexts)

Harus literally corresponds to “must” / “have to” and expresses strong obligation or necessity:

• kampanye yang baik harus praktis
  ≈ a good campaign must be practical / has to be practical

In real usage, people sometimes use harus a bit more softly, closer to “should”, but grammatically it is stronger than words like:

• sebaiknya = should / it would be better if
• perlu = need to / necessary to (often more neutral)

Yes, praktis is a loanword, related to English “practical”. Here it means:

• praktis = “practical, efficient, convenient, easy to apply in real life”

It can also mean “simple / not complicated” in everyday talk.
There is also praktikal, but praktis is far more common in sentences like this.

Breakdown:

• mudah = easy
• paham = to understand / to grasp
• memahami = to understand (something) – active
• dipahami = to be understood – passive

So mudah dipahami literally means “easy to be understood”, i.e. “easy to understand”.

Indonesian often uses a passive structure with mudah:

• mudah dimengerti / mudah dipahami = easy to understand
• mudah dilakukan = easy to do
• mudah diingat = easy to remember

An alternative is mudah dimengerti (from mengerti, also “to understand”), which is very common and very natural.

Indonesian usually does not use a separate “to be” verb (like is/are) before adjectives or many predicates. It just uses:

• subject + (modal) + adjective/predicate

Here:

• kampanye yang baik = subject
• harus = modal (“must”)
• praktis dan mudah dipahami = predicate

So:

• kampanye yang baik harus praktis
  ≈ “a good campaign must be practical”

You do not say kampanye harus adalah praktis – adalah is generally used before nouns, not adjectives.

The sentence is in neutral-to-formal standard Indonesian, suitable for:

• school / textbooks
• presentations
• writing

In casual spoken Indonesian, people might say something like:

• Guru bilang kalau kampanye yang bagus harus praktis dan gampang dimengerti.

Changes:

• menjelaskan → bilang (say/tell, informal)
• bahwa → kalau (often used as “that” in speech)
• baik → bagus (more everyday “good”)
• mudah dipahami → gampang dimengerti (more colloquial “easy to understand”)

The original sentence is perfectly natural; it just leans a bit more towards standard/formal Indonesian.