douzo saki ni tabete kudasai.

どうぞ makes the request or invitation sound more polite, welcoming, and natural. In this sentence, it gives the feeling of please, go ahead.

So 食べてください is please eat, but どうぞ先に食べてください feels more like:

• Please go ahead and eat first.
• Please, don’t wait for me.

It is very common when offering permission or encouraging someone to do something.

先に means first, ahead, or before someone else / before something else.

In this sentence, it means the other person should eat before the speaker or without waiting.

Examples of the same idea:

• 先に行ってください。 = Please go ahead.
• 先に始めます。 = I’ll start first.

So here, 先に is not just first in an abstract sense. It often has the nuance of ahead of me/us.

Here, 先 is being used as a kind of time-related noun, and に marks the point in time or order at which something happens.

So:

• 先 = ahead / earlier / before
• 先に = earlier / first / beforehand

This is similar to how に can mark a time:

• 3時に行きます。 = I’ll go at 3.
• 先に食べます。 = I’ll eat first.

In many common expressions, 先に is learned as a set phrase meaning first or ahead of time.

食べてください is the -te form + ください pattern, which is used to politely ask someone to do something.

• 食べる = to eat
• 食べて = eat... / eating...
• 食べてください = please eat

So this sentence is making a polite request or invitation.

Compared with other forms:

• 食べる = dictionary form, not a request
• 食べて = can sound casual, like eat or go ahead and eat
• 食べてください = polite please eat

Grammatically, it is an instruction/request form, but in actual use it is usually not harsh. With どうぞ and ください, it sounds polite and considerate.

In context, it often means:

• Please go ahead and eat.
• Please don’t wait for me.

So even though English learners may think please eat first sounds like an order, in Japanese this is often just a polite invitation.

Yes. You can say:

• 先に食べてください。

This still means Please eat first, and it is still polite.

However, adding どうぞ makes it softer and more hospitable. It often sounds more natural when you are encouraging someone or giving permission.

Very roughly:

• 先に食べてください。 = Please eat first.
• どうぞ先に食べてください。 = Please, go ahead and eat first.

In Japanese, adverb-like expressions such as 先に usually come before the verb they modify.

So:

• 先に食べる = eat first
• ゆっくり食べる = eat slowly
• ここで食べる = eat here

ください must come after the -te form of the verb:

• 食べてください

So the natural structure is:

• どうぞ
  • 先に
    • 食べてください

Sometimes, but the nuance is different.

• まず means first of all or to begin with
• 先に means first / ahead / before someone else or before another action

In this sentence, 先に is more natural because it suggests you eat before me / before the others / before the next thing happens.

Compare:

• まず食べてください。 = First of all, please eat.
• 先に食べてください。 = Please eat first / go ahead and eat.

まず can sound more like sequencing steps, while 先に often emphasizes order relative to another person or event.

Yes, originally 先 is a noun meaning things like ahead, front, previous, or the future destination depending on context.

Examples:

• この先 = beyond here / up ahead
• 先のこと = the future / what comes next
• 先に = first / ahead

In 先に, the noun 先 is functioning adverbially with に, so the whole phrase works like an adverb: first or ahead.

It is polite, standard Japanese.

Why?

• ください is polite
• どうぞ adds courteousness

So this would be normal to say to:

• a guest
• a coworker
• someone you want to speak politely to

A more casual version would be:

• 先に食べて。
• どうぞ先に食べて。

A stiffer or more formal version might be used in customer service or very careful speech, but the sentence you gave is already polite and very natural.

Common situations include:

• The speaker is late joining a meal and tells others not to wait.
• The speaker is still cooking or preparing food and invites the other person to start eating.
• The speaker wants to be considerate and let the other person go first.

Typical feeling:

• Please go ahead and eat without waiting for me.

So this sentence is very practical and commonly used in everyday life.