Zhǐyǒu jìzhù mìmǎ, nǐ cái kěyǐ hěn kuài dēnglù.

It is a very common pattern meaning only if / only when ... then ....

In this sentence:

• 只有记住密码，
• 你才可以很快登录。

the structure is:

• 只有 + condition
• 才 + result

So the sentence means something like:

• Only if you remember the password can you log in quickly.
• Only when you remember the password will you be able to log in quickly.

A key point: 才 usually appears in the second clause to show that the result happens only under that condition.

Chinese often leaves out the subject when it is obvious from context.

So:

• 只有记住密码，你才可以很快登录。

is understood as:

• 只有你记住密码，你才可以很快登录。

The subject 你 is omitted in the first clause because it is already clear that the sentence is about you.

This kind of omission is very natural in Chinese, especially when the same subject would appear in both clauses.

才 is very important in this pattern.

Compare:

• 只有记住密码，你才可以很快登录。
• 只有记住密码，你可以很快登录。

The version with 才 clearly expresses only then / only in that case. It matches 只有 and completes the grammar pattern.

Without 才, the sentence sounds less complete and less natural for this meaning. Native speakers strongly expect 只有……才…… together when expressing this kind of restriction.

So think of 才 as marking the result that happens only under the stated condition.

Not exactly.

• 只 usually means only / merely
• 只有 often introduces a condition meaning only if / only when / there is only

In this sentence, 只有 is not just a simple only. It introduces the condition:

• 只有记住密码 = only if you remember the password

So you cannot replace it with 只 here.

For example:

• 我只有一个问题。 = I only have one question.
• 只有努力，才会成功。 = Only if you work hard will you succeed.

Same word, but the second use is the important one here.

This is a very common learner question.

记住

Means to memorize, to retain in memory, or to successfully remember and keep it in mind.

记得

Usually means to remember in the sense of recall or not forget.

In this sentence, 记住密码 fits well because it suggests that you have the password firmly in mind.

Examples:

• 记住这个单词。 = Memorize / remember this word.
• 我记得他的名字。 = I remember his name.

Sometimes both can appear in similar situations, but 记住 often emphasizes the successful result of remembering.

Also, 住 in 记住 is a result complement, showing that the action reaches a stable result: you remember it and keep it in mind.

可以 means can / may / be able to.

In this sentence:

• 你才可以很快登录

it means then you can log in quickly or only then will you be able to log in quickly.

Yes, sometimes 可以 could be omitted:

• 只有记住密码，你才能很快登录。

This is also very natural, and many speakers might even prefer it.

Compare:

• 你才可以很快登录 = only then can you log in quickly
• 你才能很快登录 = only then are you able to log in quickly

Both are fine. The version without 可以 is a bit tighter and very common.

In Chinese, adverbial words usually come before the verb they modify.

So:

• 很快登录 = log in quickly

Structure:

• 很快 = adverbial phrase, quickly
• 登录 = verb, log in

This is normal Chinese word order:

• 他很快回来了。 = He came back quickly.
• 你可以很快找到。 = You can find it quickly.

So 很快登录 is exactly what you would expect.

Yes. 登录 is the standard modern Chinese word for log in / sign in to a website, app, or account.

Examples:

• 登录账号 = log into an account
• 登录网站 = log into a website

Be careful not to confuse it with 登陆.

登录

Used for computer systems, websites, apps, accounts.

登陆

Traditionally means to land, especially landing on shore or coming ashore. In informal digital contexts, some people type 登陆 instead of 登录, but 登录 is the standard form for log in.

The comma separates the condition clause from the main clause.

So the sentence is divided like this:

• 只有记住密码，
• 你才可以很快登录。

This makes the structure easier to read, especially with patterns like 只有……才…….

In Chinese, punctuation often helps show clause boundaries more clearly than in English. The comma here is very natural.

Yes, but not every rearrangement sounds equally natural.

A very natural variation is:

• 你只有记住密码，才可以很快登录。

This keeps the same meaning, but now 你 appears earlier.

Another very natural version is:

• 只有记住密码，你才能很快登录。

This may sound slightly smoother to many speakers.

However, you should keep the basic logic:

• 只有 + condition
• 才 + result

That relationship should stay clear.

Here it means log in quickly, not log in soon.

That is because 很快 can mean different things depending on context:

1. very fast / quickly
2. soon

In this sentence, it modifies the action 登录, so it means the manner of the action:

• 很快登录 = log in quickly

If the sentence were about time in the future, it could mean soon, but that is not the meaning here.

In speech, both are important, but 才 often gets special emphasis because it highlights the restricted result.

So a speaker may naturally stress:

• 只有 ... 才 ...

like this:

• 只有记住密码，你才可以很快登录。

This helps communicate the idea:

• not in other cases
• only in this case

You do not need exaggerated stress, but in natural speech these words often stand out slightly because they carry the sentence logic.

It is generally neutral and perfectly acceptable in everyday written or spoken Chinese.

Words like:

• 密码
• 登录

are common in modern, practical Chinese, especially in tech-related contexts.

The sentence sounds like something you might see in:

• instructions
• app guidance
• customer support
• a teaching example

It is not overly formal, but it is also not slangy.

A native speaker could say it, and it is grammatically correct. But some speakers might prefer slightly more natural versions such as:

• 只有记住密码，你才能很快登录。
• 记住密码后，你就可以很快登录。
• 只有记住密码，才能快速登录。

The best choice depends on nuance:

• 只有……才…… emphasizes only under this condition
• ……后，就可以…… emphasizes after doing this, then you can...

So your original sentence is fine, especially if the goal is to practice 只有……才…….