Než půjdeme na oslavu, vezmu si modrou bundu a dcera si do batohu dá pastelky, aby mohla kreslit pro babičku.

Než here means before. It introduces a subordinate clause: Než půjdeme na oslavu...

A useful difference from English is that Czech usually uses a full clause after než:

• Než půjdeme na oslavu... = before we go to the celebration...

English often allows before going..., but Czech normally prefers a finite verb here.

Because the action is in the future. Půjdeme is the future form of jít (to go on foot / to go).

So:

• jdeme = we are going / we go
• půjdeme = we will go

In a sentence like this, Czech commonly uses the future after než when the action has not happened yet.

With events, Czech very often uses jít na + accusative.

So:

• jít na oslavu = to go to a celebration
• jít na koncert = to go to a concert
• jít na večírek = to go to a party

The preposition na here expresses the destination as an event or activity. It is just the normal Czech pattern with many social events.

The si is a reflexive dative pronoun, often meaning something like for myself. In this sentence, vezmu si modrou bundu means that the speaker is taking/putting on the jacket for themself.

With clothes, Czech often uses verbs like:

• vzít si
• obléct si

Both can be used when someone puts something on themself.

So si does not have to be translated word-for-word every time, but it is very natural Czech here.

Because si is a clitic. Czech clitics usually go in the second position of their clause.

Compare:

• Vezmu si modrou bundu.
  The first element is vezmu, so si comes right after it.

• Dcera si do batohu dá pastelky.
  The first element is dcera, so si comes after that.

This can feel strange to English speakers, because the placement depends on clause structure, not on where you would place myself/herself in English.

Because modrou bundu is the direct object of vezmu si, so it must be in the accusative case.

Base form:

• modrá bunda = nominative singular

Object form:

• modrou bundu = accusative singular

Both the adjective and the noun change, and they must agree:

• modrá → modrou
• bunda → bundu

The verb dát has a wider meaning than just give. It can also mean put, place, or set depending on context.

So here:

• dcera si do batohu dá pastelky

means that the daughter will put the crayons into her backpack.

This is a very normal Czech use of dát. English usually separates give and put more strictly than Czech does in this kind of expression.

After do meaning into, Czech uses the genitive case.

So:

• batoh = nominative
• do batohu = genitive after do

This is the standard pattern for movement into something:

• do domu = into the house
• do školy = into the school
• do batohu = into the backpack

Here pastelky is the accusative plural because it is the direct object of dá.

The dictionary form is:

• pastelka = a crayon / colored pencil

Plural nominative:

• pastelky

Plural accusative:

• pastelky

So in this noun, the nominative plural and accusative plural happen to look the same. That is very common in Czech.

Aby introduces a purpose clause, usually meaning so that, in order that, or sometimes so ... can/could.

So:

• aby mohla kreslit = so that she can/could draw

This explains the purpose of taking the crayons.

A very important grammar point: after aby, Czech uses a special verb form built with the l-participle:

• aby mohl
• aby mohla
• aby mohli

So this is not the ordinary present tense.

It is mohla because the understood subject is dcera, which is feminine singular.

So the form agrees with the subject:

• mohl = masculine singular
• mohla = feminine singular
• mohli = plural masculine/mixed
• mohly = plural feminine/non-masculine

It is not může because after aby Czech normally does not use the ordinary present-tense form here.

Because Czech often omits subjects when they are clear from context.

Here, after dcera si do batohu dá pastelky, it is obvious that mohla refers to the daughter. So Czech does not need to repeat ona or dcera.

This is very common in Czech and is one reason Czech sentences can sound more compact than English ones.

Pro means for, and it takes the accusative case.

So:

• babička = nominative
• pro babičku = accusative after pro

In this sentence, pro babičku means that the drawing is intended for Grandma.

A useful distinction:

• pro babičku = for Grandma, intended for her
• babičce would be dative and would belong to a different construction

Because Czech uses commas to separate subordinate clauses from main clauses.

There are two subordinate clauses here:

• Než půjdeme na oslavu, ...
• ..., aby mohla kreslit pro babičku.

So the commas mark the clause boundaries:

1. after the opening než clause
2. before the aby clause

This is standard Czech punctuation.