La profesora me prestó una goma, pero yo ya tenía pegamento en la mochila.

In Spain, una goma commonly means an eraser.

This is a very important regional vocabulary point, because in some Latin American countries goma does not usually mean eraser, and in some contexts it can even mean something completely different. If you want a safer, more widely understood word, you may also see borrador or goma de borrar, but in Spain goma is very normal for eraser.

Me means to me.

So:

• La profesora prestó una goma = The teacher lent an eraser
• La profesora me prestó una goma = The teacher lent me an eraser

Spanish often uses an indirect object pronoun like me, te, le, nos, os, les before the verb to show to whom something is given, lent, shown, etc.

Here:

• me = to me
• prestó = lent

So literally, it is something like: The teacher to-me lent an eraser.

Prestó is the preterite form of prestar.

• prestar = to lend
• prestó = he/she lent

It is preterite because it describes a completed action in the past: the teacher lent the eraser at a specific moment.

Tenía is the imperfect form of tener, and it is used here because it describes a background situation or an existing state in the past.

Compare:

• yo ya tenía pegamento = I already had glue
• yo tuve pegamento = I had glue (more like a completed event, less natural here)

In this sentence, the speaker is not talking about the moment when they got the glue. They are talking about the fact that they already had it. That is why tenía sounds natural.

A very common pattern is:

• something happened → preterite
• the background situation that was already true → imperfect

So:

• La profesora me prestó una goma = completed event
• yo ya tenía pegamento = ongoing background state

Yes, it could.

Spanish often drops subject pronouns because the verb ending already tells you who the subject is:

• tenía can mean I had, he had, or she had, depending on context
• here, context makes I had clear

So pero ya tenía pegamento is perfectly natural.

The sentence uses yo for emphasis or contrast:

• La profesora me prestó una goma, pero yo ya tenía pegamento...

That yo helps underline the contrast: but I already had glue.

Ya here means already.

So:

• yo tenía pegamento = I had glue
• yo ya tenía pegamento = I already had glue

It shows that the glue was in the backpack before the teacher lent the eraser.

Here pegamento is being used as an uncountable noun, like glue in English.

So Spanish often says:

• tenía pegamento = I had glue

rather than:

• tenía un pegamento

You would use un pegamento only in a more specific sense, for example if you mean a type of glue or a glue product.

Because en means in / inside / in the location of, which is what you need here.

• en la mochila = in the backpack

A usually indicates movement toward something:

• voy a la mochila would mean something like I go to the backpack, which does not fit here

Since the glue was located inside the backpack, en is the correct preposition.

Spanish often uses the definite article with professions or roles when talking about a specific person:

• la profesora = the teacher

Here it refers to a particular teacher already known in the situation.

If you said just Profesora by itself, that could sound like direct address:

• Profesora, tengo una pregunta = Teacher, I have a question

So in this sentence, la profesora is correct because it is the subject of the sentence, not someone being spoken to directly.

No. This is a very common confusion.

• prestar = to lend
• pedir prestado or sometimes tomar prestado = to borrow

So:

• La profesora me prestó una goma = The teacher lent me an eraser
• Yo pedí prestada una goma = I borrowed an eraser

English uses two different verbs, and Spanish does too, but learners sometimes mix them up.

Yes, absolutely.

• en la mochila = in the backpack
• en mi mochila = in my backpack

Both work.

Using la mochila can sound natural if it is obvious whose backpack it is from context. Spanish often uses the definite article where English would prefer a possessive.

This is similar to things like:

• Me duele la cabeza = My head hurts
• literally: The head hurts me

So en la mochila is normal if the backpack clearly belongs to the speaker.

The basic structure is:

• La profesora = subject
• me = indirect object pronoun
• prestó = verb
• una goma = direct object

Then:

• pero = but
• yo = subject
• ya = already
• tenía = verb
• pegamento = object
• en la mochila = location

So the sentence follows a pretty normal Spanish word order:

Subject + pronoun + verb + object

and then

pero + subject + adverb + verb + object + location

The accent mark distinguishes the preterite form from other forms and shows the stress.

• prestó = he/she lent
• presto without an accent is a different word/form and is not the same here

In Spanish verbs, accent marks are often important for identifying tense and person, especially in the preterite:

• hablo = I speak
• habló = he/she spoke

So prestó must keep the accent.