Learn Hardcore Japanese: sensei ha maikai wakariyasui setumei wo site kuremasu. - The teacher gives an easy-to-understand explanation every time.

先生は means “as for the teacher” or “the teacher (speaking of them)”.
It doesn’t strictly mark the grammatical subject; it marks what we’re talking about.

In this sentence, we’re talking about the teacher, and then saying what they do:
先生は … してくれます。 → “As for the teacher, (they) do X (for me/us).”

Why is there no word for “I” or “me” in this sentence?

Japanese often omits pronouns when they’re obvious from context.

The sentence literally feels like:

“As for the teacher, every time, easy-to-understand explanations do-(for me/us).”

The くれます part (a benefactive verb) already implies “for me / for us (the speaker’s side)”, so you don’t need 私に.
Listeners naturally understand that the teacher explains things to the speaker (or their group).

Does 先生 always mean “teacher”? Could it also be “doctor”?

先生 (せんせい) is a respectful title used for:

School teachers
Professors
Doctors
Some other professionals (e.g., lawyers, politicians, artists) in certain contexts

In a textbook example like this, it almost always means “(my/our) teacher”.
If the context were a hospital, it could easily mean “doctor”. The sentence structure itself doesn’t change; context decides the exact role.

What’s the nuance of 毎回 compared to words like いつも or 毎日?

毎回 (まいかい) = “every time (something happens)”
- Focuses on each occurrence of some repeated situation.
- E.g., every time we have class, every time I ask a question, etc.
いつも = “always / usually”
- More general: “as a rule”, “habitually”.
毎日 = “every day”
- Specifically refers to days.

So:

先生は毎回分かりやすい説明をしてくれます。
→ “Every time (we have class / I ask), the teacher gives an easy-to-understand explanation.”
先生はいつも分かりやすい説明をしてくれます。
→ “The teacher always gives easy-to-understand explanations.” (general habit, not tied to a specific “event”)

How does 分かりやすい work? Why does it mean “easy to understand”?

分かりやすい is formed as:

Verb 分かる (to understand)
- suffix 〜やすい (easy to do)

So:

分かる → 分かり (stem form) + やすい
→ 分かりやすい = “easy to understand”

This is a common pattern:

使う (to use) → 使いやすい (easy to use)
読みます (to read) → 読みやすい (easy to read)
飲む (to drink) → 飲みやすい (easy to drink)

In the sentence, 分かりやすい is an i-adjective describing 説明:
分かりやすい説明 = “an easy-to-understand explanation”.

Is 分かりやすい an adjective? Why doesn’t it need な before 説明?

Yes, 分かりやすい is an い-adjective.

い-adjectives directly modify nouns:
大きい家 (big house), 新しい本 (new book), 分かりやすい説明 (easy-to-understand explanation)
な-adjectives need な before nouns:
静かな部屋 (quiet room), 便利な道具 (convenient tool)

Since 分かりやすい ends in 〜い and behaves like an い-adjective, it goes directly before 説明 without な.

Why do we say 説明をしてくれます instead of just 説明します?

Both are possible, but they have different nuances.

説明します = “(I/they) explain.”
- Simple explain action, neutral.
説明をします = same meaning; 説明をする is the “noun + する” pattern.
(説明する is also fine and very common.)
説明をしてくれます adds:
- The 〜てくれる benefactive form: “do (something) for me / us”
- A sense of kindness or favor.

So 説明をしてくれます feels like:

“(The teacher) gives (me/us) an explanation”
or “(The teacher) kindly explains (it) to us.”

It puts a little emotional focus on the fact that the teacher is doing something beneficial for the speaker.

What exactly does 〜てくれます mean here?

〜てくれる / 〜てくれます is the benefactive form:

Pattern: [someone] が [me/us] に [action] 〜てくれる
Meaning: “[Someone] does [action] for me/us (as a favor, beneficially).”

In this sentence:

The teacher = the doer (subject/topic: 先生は)
The receiver = the speaker (and/or their group)
Action = 説明をする → 説明をして

So してくれます means “does (it) for me/us”, and with the whole phrase:

分かりやすい説明をしてくれます。
→ “(They) give us easy-to-understand explanations.”
→ “(They) explain things clearly for us.”

That for us / for me nuance is built into くれる.

Who is the “receiver” of してくれます if it’s not written?

By default, 〜てくれる assumes the receiver is:

The speaker (私), or
Someone in the speaker’s close “in-group” (like family, friends, the class the speaker belongs to)

So even without 私に, Japanese listeners understand:

“The teacher gives me/us easy-to-understand explanations.”

If you really wanted to specify, you could say:

先生は毎回私たちに分かりやすい説明をしてくれます。
(“The teacher gives us easy-to-understand explanations every time.”)

Why is it 説明をしてくれます instead of 説明してくれます? Is there a difference?

Both are correct:

説明をしてくれます
説明してくれます

説明をする is a noun + を + する verb combination.
In casual and even formal speech, people often drop the を:

説明をする → 説明する
説明をしてくれる → 説明してくれる

Nuance:

説明をしてくれます feels slightly more formal/emphatic.
説明してくれます is a bit more compact and very common.

Meaning-wise, there’s no real difference in most contexts.

Why is the verb in してくれます in present form if this is a habitual action?

Japanese “present tense” (〜ます / dictionary form) covers both:

Present and future
Single actions and habitual actions

So:

先生は毎回分かりやすい説明をしてくれます。
→ “The teacher gives easy-to-understand explanations every time.”
(Understood as a repeated, habitual behavior because of 毎回.)

You don’t need a separate tense form for “does habitually”; the context word 毎回 already signals the repeated nature.

Could we also say 先生は毎回分かりやすく説明してくれます? What’s the difference?

Yes, that’s also correct and very natural:

分かりやすい説明をしてくれます
→ literally: “(They) do an easy-to-understand explanation (for us).”
→ focuses on the explanation as a thing.
分かりやすく説明してくれます
→ 分かりやすく is the adverb form of 分かりやすい.
→ literally: “(They) explain in an easy-to-understand way (for us).”
→ focuses more on the manner of explaining.

In everyday usage, the overall meaning is almost the same:
“The teacher explains things clearly every time.” Both are fine.