Deja la mochila allí, por favor.

Deja is the tú imperative form of dejar.

• dejar = the infinitive, to leave / to put down
• dejas = you leave (present tense, statement)
• deja = leave! / put it down! (command to one person you address as tú)

So in this sentence, deja is giving an instruction to one person in an informal way.

It is the affirmative informal singular command: the command used with tú.

For most regular -ar verbs, the tú affirmative command looks like the él/ella/usted present form:

• dejar → él deja
• command to tú → deja

So:

• Deja la mochila allí. = command to one person you know, a friend, child, classmate, etc.

In Spain, if you were talking to:

• usted (formal singular): Deje la mochila allí, por favor.
• vosotros (informal plural): Dejad la mochila allí, por favor.
• ustedes (formal plural): Dejen la mochila allí, por favor.

Spanish usually omits subject pronouns when they are not needed, because the verb form already shows who the subject is.

Here, deja already tells you the command is for tú, so tú is unnecessary.

You could say:

• Tú deja la mochila allí.

But that would usually add emphasis, contrast, or impatience. In normal speech, just Deja la mochila allí is more natural.

Spanish uses articles like el / la / los / las more often than English does.

Here, la mochila means the backpack. Even if English might sometimes say Leave your backpack there or just Leave the backpack there, Spanish often keeps the article with a specific object being talked about.

So la mochila sounds natural because it refers to a particular backpack that both speakers understand from context.

Depending on context, Spanish could also say:

• Deja tu mochila allí. = Leave your backpack there.
• Deja una mochila allí. = Leave a backpack there.

But la mochila is perfectly normal if the backpack is already known.

In this sentence, dejar can feel closer to put or set down in natural English, depending on context.

Dejar often means:

• to leave
• to put / to set down
• to let (in other contexts)

Here, with a physical object and a place, it means something like:

• leave the backpack there
• put the backpack there
• set the backpack down there

So this is a very common use of dejar with objects.

These are all adverbs of place, but they point to different distances.

A simple way to think about them is:

• aquí = here (near the speaker)
• ahí = there (near the listener / not far away)
• allí = over there (farther away)

So Deja la mochila allí suggests a place that is not here and usually some distance away.

In Spain, learners often also hear allá, which is similar to allí, though sometimes a bit less exact and more like over there in a broader sense.

Because allí is already an adverb meaning there / over there, and dejar can take a direct object plus a place adverb directly.

Structure:

• Deja = command
• la mochila = direct object
• allí = place

So Deja la mochila allí is complete as it is.

You do not need en before allí in this structure.

Compare:

• Déjalo allí. = Leave it there.
• Ponlo allí. = Put it there.

But with a noun phrase for location, you often do use a preposition:

• Deja la mochila en la mesa. = Leave the backpack on the table.

Por favor makes the command more polite, like please.

It can appear in different positions:

• Deja la mochila allí, por favor.
• Por favor, deja la mochila allí.
• Deja, por favor, la mochila allí. (possible, but less common in everyday speech)

The most natural positions are usually:

• at the beginning
• at the end

Putting it at the end, as in your sentence, sounds very normal.

In Spain, deja is pronounced approximately DEH-ha, but with a stronger throaty j sound than English h.

Breakdown:

• de = like deh
• j = the Spanish j, a rough sound made farther back in the mouth
• a = ah

So roughly: DEH-ha

The stress is on the first syllable: DE-ja.

Mochila is pronounced approximately:

mo-CHEE-la

Breakdown:

• mo = moh
• chi = chee
• la = lah

The stress is on chi: mo-CHI-la

The ch sound is like English ch in chair.

Usually approximately:

ah-YEE

In most of Spain, ll is pronounced like a y sound, so:

• allí ≈ ah-YEE

The accent mark on í shows that the stress falls on the last syllable:

• a-LLÍ

In some parts of Spain, some speakers may pronounce ll differently, but ah-YEE is a very good standard pronunciation for learners.

The accent mark shows that the stress is on the final syllable:

• a-llí

Without the written accent, Spanish stress rules would not give the same pronunciation.

So the accent is there to mark the correct stress. It is an important part of the spelling.

Yes. Déjala allí is very common.

It means the same thing, but now the direct object la (it) is attached to the command:

• Deja la mochila allí. = Leave the backpack there.
• Déjala allí. = Leave it there.

Why the accent in Déjala?

When pronouns attach to an affirmative command, the stress pattern can change, so Spanish adds a written accent to keep the original stress:

• deja
• déjala

So both are correct, but Déjala allí is used when the object is already clear from context.

It sounds natural. Spanish often uses the imperative more directly than English does, especially with por favor added.

• Deja la mochila allí, por favor. is polite and normal.
• Without por favor, it can sound more direct, depending on tone.
• With a friendly tone, it is perfectly fine in everyday situations.

If you wanted to sound softer, you could also say things like:

• Pon la mochila allí, por favor.
• ¿Puedes dejar la mochila allí, por favor?

But your sentence is absolutely natural in Spain.

Yes, often.

• Deja la mochila allí = Leave/put the backpack there
• Pon la mochila allí = Put the backpack there

The difference is subtle:

• poner focuses more on placing something
• dejar often focuses on leaving it in that place

In many everyday situations, both work. But dejar is especially natural when you mean set it down and leave it there.

Yes. In Spain, vosotros is the normal informal plural form.

So if you were speaking to more than one person informally, you would say:

• Dejad la mochila allí, por favor.

That is very typical in Spain.

In most of Latin America, people would usually say:

• Dejen la mochila allí, por favor.

So your original sentence is fully compatible with Spain Spanish, and the plural version in Spain would normally use vosotros.