Aldonu la pizojn.

Aldonu is the verb aldoni in the imperative / jussive form.

• aldoni = to add
• aldonu = add! / let ... add

In this sentence, it is a direct command, so Aldonu means Add.

The ending -u is used in Esperanto for:

• commands: Venu! = Come!
• requests: Helpu min. = Help me.
• suggestions or wishes: Ni iru. = Let’s go.

So Aldonu la pizojn. is a command: Add the peas.

Esperanto word order is fairly flexible, but the most common order in simple commands is often just:

Verb + object

So:

• Aldonu la pizojn. = Add the peas.

This is very natural in Esperanto. You could change word order in some contexts, but this is the normal straightforward way to give an instruction.

La is the definite article, meaning the.

So:

• pizoj = peas
• la pizoj = the peas

Esperanto has only one article, la, and it does not change for singular, plural, or case.

That means:

• la pizo = the pea
• la pizoj = the peas
• la pizon = the pea as a direct object
• la pizojn = the peas as a direct object

The ending -jn is made of two separate parts:

• -j = plural
• -n = accusative, used for a direct object

So:

• pizo = pea
• pizoj = peas
• pizon = pea (direct object)
• pizojn = peas (direct object)

In Aldonu la pizojn, the peas are the thing being added, so they are the direct object. That is why pizojn needs -n.

Yes, that would be ungrammatical in standard Esperanto.

Because the peas are the direct object of add, they need the accusative ending -n:

• correct: Aldonu la pizojn.
• incorrect: Aldonu la pizoj.

A native English speaker may want to leave off -n, because English does not mark direct objects this way, but in Esperanto this ending is important.

The dictionary form is pizo.

To get from the dictionary form to pizojn:

1. pizo = pea
2. pizoj = peas
3. pizojn = peas as the direct object

This is a very common Esperanto pattern:

• singular noun: -o
• plural: -oj
• accusative singular: -on
• accusative plural: -ojn

A simple English-friendly guide is:

ahl-DOH-noo lah pee-ZOYN

A few useful pronunciation notes:

• a sounds like a in father
• o sounds like o in told, but pure and short
• u sounds like oo in food
• z is like English z
• oj sounds roughly like English oy

Stress in Esperanto normally falls on the second-to-last syllable:

• alDOnu
• PIzojn

So the stress is:

• alDOnu
• la
• PIzojn

It can be either.

Esperanto verbs do not change depending on the subject. So Aldonu can mean:

• Add! said to one person
• Add! said to several people
• Please add in a recipe or instruction

If you want to make the subject explicit, you can add a pronoun:

• Vi aldonu la pizojn. = You add the peas. / Add the peas.

But in commands, the pronoun is usually omitted.

In theory, yes: the -u form can also express a wish or instruction involving other persons.

For example:

• Li aldonu la pizojn. = Let him add the peas.
• Ŝi aldonu la pizojn. = Let her add the peas.

But Aldonu la pizojn. by itself is normally understood as a direct command to the listener: Add the peas.

Yes, absolutely.

This is a very natural recipe or instruction style in Esperanto. Recipes often use the -u form for step-by-step commands:

• Tranĉu la cepojn. = Chop the onions.
• Aldonu la pizojn. = Add the peas.
• Miksu bone. = Mix well.

So this sentence sounds exactly like the kind of instruction you would expect in cooking directions.