Learn Hardcore Chinese: yìfāngmiàn wǒ xiǎng zài gōngyuán sànbù, yìfāngmiàn wǒ xūyào zài jiā rènzhēn fùxí zhōngwén. - On one hand I want to take a walk in the park; on the other hand I need to stay home and seriously review Chinese.

一方面 introduces one “side” or “aspect” of a situation, similar to “on the one hand” in English.
It signals that another, often contrasting or complementary, aspect is coming in the next clause.
So 一方面我想在公园散步，一方面我需要在家认真复习中文 sets up a contrast between what you want to do and what you need to do.

Why is 一方面 repeated? Shouldn’t it be 一方面…另一方面…?

Both patterns exist, but they have slightly different feels:

一方面……一方面…… often presents two aspects that coexist or are being weighed against each other.
一方面……另一方面…… more clearly matches English “on the one hand… on the other hand…”.

In your sentence, 一方面……一方面…… is acceptable and natural, especially in spoken Chinese.
If you change the second to 另一方面, it becomes a bit more formal and explicitly contrastive, but the meaning is almost the same here.

Could I say 我一方面想在公园散步，一方面需要在家认真复习中文? Where do 一方面 and 我 usually go?

Yes, 我一方面想在公园散步，一方面需要在家认真复习中文 is also correct and natural.
Both of these are fine:

一方面我想……，一方面我需要……
我一方面想……，一方面需要……

Placing 一方面 directly before the verb phrase (想 / 需要) tends to sound slightly more natural than splitting 我 from its verb, but in this short sentence both word orders are common.

Why is the word order 我想在公园散步 and not 我在公园想散步?

我想在公园散步 is the normal order: subject + mental verb + place phrase + main action.

我想在公园散步 = I want to take a walk in the park.
我在公园想散步 literally sounds like “I, in the park, feel like taking a walk,” and is unusual because 想散步 describes a desire, not an action happening in the park.

The place 在公园 modifies the actual action 散步, not the mental state 想, so it stays close to 散步.

Why does 在 come before 公园 and 家? Could I say just 想公园散步 or 需要家复习?

在 + place is the standard way to mark location in Chinese:

在公园散步 = take a walk in the park
在家复习中文 = review Chinese at home

You can’t just say 想公园散步 or 需要家复习; without 在, 公园 and 家 don’t function as proper location phrases here.
Think of 在公园 and 在家 as “at/in the park” and “at home.”

Why is there no word like English “to” before 散步 and 复习?

Chinese verbs don’t need an infinitive marker like English “to.”
想散步 is simply “want (to) walk,” and 需要复习 is “need (to) review.”
The sense of “to do something” is built into the pattern (想/需要/要/能/会 + Verb), so no extra word is added.

What’s the difference between 想, 要, and 需要 here?

In this sentence:

想 expresses a desire or wish: 我想在公园散步 = I would like to take a walk.
需要 expresses a need or necessity: 我需要在家复习中文 = I need to review Chinese.
要 can mean “want to” or “going to,” and can sound more definite than 想.

You could say 我一方面想在公园散步，一方面要在家认真复习中文, but 需要 emphasizes obligation/necessity more clearly than 要.

What does 认真 (rènzhēn) add? Could I just say 复习中文?

认真 means “seriously,” “conscientiously,” “with effort.”
认真复习中文 means you’re not just reviewing; you’re doing it carefully and with focus.
You can say simply 在家复习中文, but you lose the nuance that you plan to study in a focused, diligent way.
Grammatically both are correct; 认真 just adds attitude/intensity.

What’s the difference between 复习中文 and 学/学习中文?

学习中文 / 学中文 = to learn/study Chinese (in general, including new material).
复习中文 = to review Chinese; go over what you’ve already learned.

In this sentence, 复习中文 implies you already know some Chinese and need to go back over it (for an exam, homework, consolidation, etc.).
Using 学习中文 would shift the meaning to “study Chinese” more generally, not specifically “review.”

Can I drop the second 我 and say 一方面我想在公园散步，一方面需要在家认真复习中文?

Yes, that’s fine and quite natural.
Chinese often drops repeated subjects when the subject is clearly understood from context.
Both are correct:

一方面我想在公园散步，一方面我需要在家认真复习中文 (repeats 我)
一方面我想在公园散步，一方面需要在家认真复习中文 (omits second 我)

The version without the second 我 is a bit more concise; the meaning is unchanged.

Is 中文 the same as 汉语 in this sentence? Which is more natural?

In this context, 中文 and 汉语 can both be used, but they’re not completely identical in usage:

汉语: specifically the Chinese spoken language (especially Mandarin in many contexts).
中文: Chinese language in a broad sense, often including reading/writing; it can mean “the Chinese subject” at school.

For “reviewing Chinese (as a subject or course),” 复习中文 is very natural and commonly used.
复习汉语 is also grammatically fine but sounds slightly more textbook-like or technical in everyday speech.

What’s the difference between 散步 and 走路? Could I say 在公园走路?

散步 means “to take a walk / go for a stroll,” usually for relaxation or light exercise.
走路 is more general: “to walk (on foot)” as a mode of movement.

In this sentence, 在公园散步 fits best because it’s clearly a leisure activity.
You can say 在公园走路, but it sounds more like “walking in the park (as a way of moving)” and less like the deliberate activity of “going for a walk.”

How do we know if this sentence is about the present or the future, since there’s no tense like in English?

Chinese verbs don’t change form for tense.
Context and time words (like 今天, 明天, 现在) usually tell you whether it’s past, present, or future.
Here, 想 and 需要 describe the speaker’s current state: “I (currently) want/need…,” and that often implies a near-future decision or plan.
If you add 今天 or 明天, it becomes clearer, e.g. 今天一方面我想……，一方面我需要…….

Could I say 在家里认真复习中文 instead of 在家认真复习中文? Is there a difference?

Yes, 在家里认真复习中文 is also correct.

在家 is very common and neutral: “at home.”
在家里 can feel a bit more specific or slightly more spoken/emphatic, like “inside the home / inside the house,” but often the difference is minimal.

In everyday speech, 在家 is more frequent and sounds perfectly natural here.