Mi madre guarda las galletas en un tarro de vidrio.

In modern Spanish, possessives like mi, tu, su, nuestro normally replace the article before a noun.

So you say:

• mi madre = my mother
• tu casa = your house

Not:

• la mi madre ❌

English speakers often expect both, but Spanish usually uses just the possessive.

Here, guarda means keeps or stores.

The verb is guardar, which can mean:

• to keep
• to store
• to put away
• sometimes to save

In this sentence, Mi madre guarda las galletas..., the idea is that she keeps the biscuits/cookies in a glass jar.

Because the subject is mi madre, which is he/she/it form in grammar terms: third person singular.

So the present tense of guardar is:

• yo guardo = I keep
• tú guardas = you keep
• él/ella guarda = he/she keeps

Since mi madre = she, you use guarda.

Spanish uses articles more often than English does.

Las galletas means the biscuits/cookies. In a sentence like this, Spanish usually includes the definite article because it refers to a specific set of biscuits already understood in context.

English might sometimes say:

• My mother keeps cookies in a glass jar

But Spanish often prefers:

• Mi madre guarda las galletas en un tarro de vidrio

So even when English sounds more natural without the, Spanish often keeps el/la/los/las.

Tarro is a masculine singular noun, so it takes the masculine singular indefinite article un.

• un tarro = a jar
• una caja = a box

You can often tell gender from the ending, though not always. Since tarro ends in -o, it is very commonly masculine.

Literally, it means of glass.

Spanish often uses de + material to describe what something is made of:

• un tarro de vidrio = a glass jar
• una mesa de madera = a wooden table
• una cuchara de metal = a metal spoon

So Spanish says jar of glass, where English usually says glass jar.

Because in Spanish, material descriptions usually come after the noun:

• un tarro de vidrio
• una puerta de madera
• un anillo de oro

English often puts that kind of information before the noun:

• glass jar
• wooden door
• gold ring

So this is a very normal word-order difference between the two languages.

En here means in.

• guardar algo en un tarro = to keep something in a jar

It shows location or container. This is the standard preposition to use here.

You could also sometimes hear dentro de (inside), but en is simpler and more natural in an ordinary sentence like this.

Yes. Galletas is a general word that can correspond to cookies or biscuits, depending on the variety of English and the exact type of food.

For a learner of Spanish from Spain, the important point is that galletas is the normal everyday word.

It is natural, but there are other possible words depending on the exact container.

In Spain, you may also hear:

• tarro = jar
• bote = jar/container/tub
• frasco = jar/bottle, often a smaller container

Tarro de vidrio is completely understandable and natural. In some contexts, a Spaniard might also say bote de cristal.

Both can be used, but they are not always exactly the same in every context.

• vidrio = glass as a material
• cristal = glass, often when talking about glass objects, panes, or a more everyday way of referring to glass in Spain

In Spain, many speakers would naturally say un tarro de cristal.
But un tarro de vidrio is still correct and clearly means a jar made of glass.

So this is partly a vocabulary choice.

Yes, Spanish word order is somewhat flexible, but the original order is the most neutral and natural:

• Mi madre guarda las galletas en un tarro de vidrio.

You could also say:

• Mi madre guarda en un tarro de vidrio las galletas.

That is grammatically possible, but it sounds more marked or stylistically different. A learner should normally stick with the original order unless there is a special reason to emphasize something.

Because mi madre is the noun phrase that matches the verb guarda.

Spanish often does not require subject pronouns like ella, so the subject is often just the noun itself:

• Mi madre guarda... = My mother keeps...

Then las galletas is the direct object: the thing being kept.

So the sentence structure is:

• Mi madre = subject
• guarda = verb
• las galletas = direct object
• en un tarro de vidrio = prepositional phrase showing location

Yes, but the tone changes slightly.

• mi madre = my mother, a bit more neutral or formal
• mi mamá = my mum/mom, more familiar and affectionate

Both are correct. In Spain, madre is common and neutral, while mamá is also very common in everyday family speech.