Si quieres alimentar a la mascota, deja el pienso junto a la jaula.

Si quieres means if you want. In Spanish, si is used to introduce a real or possible condition.

Here, si quieres alimentar a la mascota means if you want to feed the pet.

This uses the present indicative after si, which is normal for real or likely situations:

• Si quieres, te ayudo. = If you want, I’ll help you.
• Si tienes tiempo, ven. = If you have time, come.

Spanish does not use a future form after si in this kind of sentence.

Because la mascota is a living being, Spanish usually uses the personal a before a specific person or animal when it is the direct object.

So:

• alimentar a la mascota = correct
• ver a mi hermano = correct
• quiero a mi perro = correct

This a often appears with people and pets, especially when they are specific and identifiable.

Alimentar means to feed or to nourish. It is correct, but it can sound a little more formal or general than everyday spoken Spanish.

In very natural everyday Spanish, especially in Spain, people often say:

• dar de comer a la mascota = to feed the pet

So these are both possible:

• Si quieres alimentar a la mascota...
• Si quieres dar de comer a la mascota...

The sentence you were given is perfectly correct; dar de comer is just often more conversational.

Deja here is the affirmative tú command of dejar.

It is telling someone directly:

• deja el pienso junto a la jaula = leave/put the feed next to the cage

Compare:

• tú dejas = you leave / you are leaving → statement
• deja = leave / put → command to tú
• deje = command for usted

So:

• Deja el pienso... = informal singular
• Deje el pienso... = formal singular

Here dejar means to leave or to put something somewhere.

So deja el pienso junto a la jaula means:

• leave the pet food next to the cage
• or more naturally in some contexts, put the pet food next to the cage

Spanish dejar is very common and can mean:

• to leave
• to put
• to let/allow in other contexts

So the exact English translation depends on context.

In Spain, pienso usually means animal feed, especially dry pet food or kibble.

So in this sentence, el pienso is the food for the pet.

This is very common in Spain:

• pienso para perros = dog food
• pienso para gatos = cat food

In other Spanish-speaking countries, people may prefer other expressions such as:

• comida para mascotas
• alimento para mascotas
• comida balanceada in some regions

But in Spain, pienso is very natural.

Junto a means next to, beside, or right by.

So:

• junto a la jaula = next to the cage

It is very similar to:

• al lado de la jaula

Both are correct. Junto a can sound a little more compact or slightly more formal, but both are common.

Examples:

• El libro está junto a la lámpara.
• El libro está al lado de la lámpara.

Both mean The book is next to the lamp.

Spanish nouns have grammatical gender, so they take different articles:

• la mascota → feminine
• el pienso → masculine
• la jaula → feminine

You usually have to learn the noun together with its article:

• la mascota
• el pienso
• la jaula

That is the safest habit, because grammatical gender does not always match any logical idea in English.

Yes. Pon would also be very natural.

Difference:

• deja el pienso... = leave/put the feed...
• pon el pienso... = put the feed...

Pon focuses more directly on placing it somewhere. Deja can suggest leaving it there.

In many situations, both would sound fine.

This is a very normal Spanish structure:

1. condition
2. main command

So:

• Si quieres alimentar a la mascota = condition
• deja el pienso junto a la jaula = instruction

English does the same thing:

• If you want to feed the pet, leave the feed next to the cage.

You could also reverse the order in Spanish:

• Deja el pienso junto a la jaula si quieres alimentar a la mascota.

But the original version sounds more natural because it sets up the condition first.

Usually, yes. Mascota normally means pet.

It refers to an animal kept at home as a companion:

• un perro as a pet
• un gato as a pet
• un hámster as a pet

In this sentence, la mascota is just the pet. It does not specify what kind of animal it is.

The comma separates the if-clause from the main clause:

• Si quieres alimentar a la mascota,
• deja el pienso junto a la jaula.

This is also common in English:

• If you want to feed the pet, leave the feed next to the cage.

It helps show that the first part is the condition and the second part is the instruction.