Min mor lægger et æg og et æble i min madpakke, så jeg ikke bliver sulten i skolen.

Because lægge means to lay / to put something somewhere, while ligge means to lie / to be located.

In this sentence, the mother is actively putting the egg and the apple into the lunchbox, so Danish uses lægger:

• Min mor lægger et æg ... i min madpakke = My mother puts an egg ... in my lunchbox

Compare:

• Jeg lægger bogen på bordet = I put the book on the table
• Bogen ligger på bordet = The book is lying / is on the table

This is a very common Danish distinction, and it often feels tricky for English speakers.

Madpakke is a very common Danish word meaning packed lunch, lunchbox, or the food packed to take with you, especially to school or work.

It is made up of:

• mad = food
• pakke = package / pack

So min madpakke literally suggests my food pack, but in natural English it is usually my lunchbox or my packed lunch, depending on context.

Because both æg (egg) and æble (apple) are neuter nouns in Danish, and neuter singular indefinite nouns take et.

Danish has two grammatical genders for common nouns:

• en words
• et words

So:

• et æg = an egg
• et æble = an apple

You simply have to learn whether a noun is an en noun or an et noun.

For comparison:

• en bog = a book
• et hus = a house

Because mor and madpakke are both common gender nouns, so the possessive form used is min.

The possessive forms are:

• min for en-words
• mit for et-words
• mine for plural

Examples:

• min mor = my mother
• min madpakke = my lunchbox
• mit æble = my apple
• mine bøger = my books

So the possessive agrees with the gender/number of the noun that follows.

This is because Danish word order changes in subordinate clauses.

Here, så means so (that) and introduces a subordinate clause:

• så jeg ikke bliver sulten i skolen = so that I do not get hungry at school

In Danish subordinate clauses, sentence adverbs like ikke usually come before the finite verb:

• jeg ikke bliver sulten

Compare that with a main clause:

• Jeg bliver ikke sulten = I do not get hungry

So:

• main clause: subject + verb + ikke
• subordinate clause: subject + ikke
  • verb

This is one of the most important word-order patterns in Danish.

Literally, bliver sulten means becomes hungry.

• bliver = becomes / gets / is becoming
• sulten = hungry

In natural English, we usually say get hungry, so:

• jeg bliver sulten = I get hungry

Danish often uses blive where English uses get:

• blive træt = get tired
• blive glad = become happy
• blive syg = get sick

Because jeg is singular, and the adjective is describing a singular person.

In this sentence:

• jeg bliver sulten = I get hungry

Here sulten is the common singular form used with a person.

Compare:

• Jeg er sulten = I am hungry
• Vi er sultne = We are hungry

So sulten is singular, while sultne is plural or sometimes used in definite contexts.

Because Danish often omits the article with places like school, church, town, etc. when talking about the institution or the usual activity connected with it.

So:

• i skolen can mean at school / in school

This is similar to English, where we often say at school rather than at the school, depending on meaning.

Compare:

• Han er i skole = He is at school / in school
• Han står ved skolen = He is standing by the school

The second one refers more to the physical building, while the first refers to the institution/activity.

Danish is simply saying an egg and an apple, so it uses singular nouns because each item is one thing:

• et æg = an egg
• et æble = an apple

English could also say:

• My mother puts an egg and an apple in my lunchbox

So the Danish grammar here is very straightforward. If there were more than one, Danish would use plurals:

• æg can also be plural in form depending on context
• æbler = apples

But in this sentence, singular is correct because it means one egg and one apple.

Because Danish, like English, normally connects two nouns with a single og (and):

• et æg og et æble = an egg and an apple

Each noun still keeps its own article because they are two separate indefinite items.

Compare:

• en bog og en blyant = a book and a pencil
• et æg og et æble = an egg and an apple

So the structure is completely normal:
article + noun + og + article + noun

Here så means so, more specifically so that or with the result/purpose that.

So the sentence means:

• Min mor lægger et æg og et æble i min madpakke, så jeg ikke bliver sulten i skolen.
• My mother puts an egg and an apple in my lunchbox so that I do not get hungry at school.

In other contexts, så can also mean other things, such as:

• then
• so
• thus
• very (in some expressions)

But in this sentence, it is linking the action with its purpose/result.

These are both words with æ, which can be difficult for English speakers.

• æ is a front vowel somewhat like the vowel in English cat, but not exactly the same.
• æg is pronounced roughly like eye
  • a soft/guttural ending in some varieties, though that is only an approximation.
• æble is roughly EH-bluh, but again not exactly.

A few useful pronunciation notes:

• æg is a very short word, and the final consonant may sound softer than an English g
• æble has two syllables: æ-ble
• The b in æble is not as strongly released as in English

The best way to learn these is by listening to native audio and repeating them many times.

Yes, it is a perfectly normal and natural sentence.

It sounds like standard everyday Danish:

• Min mor = my mother
• lægger ... i min madpakke = puts ... in my lunchbox
• så jeg ikke bliver sulten = so I do not get hungry
• i skolen = at school

A Dane might also express the idea in slightly different ways, for example:

• Min mor pakker et æg og et æble i min madpakke ...
• Min mor giver mig et æg og et æble med i madpakken ...

But the original sentence is absolutely natural and good Danish.