Než dám košile do pračky, dívám se, jestli v nich nic není.

Because dát is a perfective verb, and Czech often uses a present-tense form of a perfective verb to talk about a future completed action.

So:

• Než dám košile do pračky... = Before I put the shirts in the washing machine...

Here, the action of putting the shirts in is seen as a single completed event.
If you said dávám, that would be the imperfective verb dávat, which would sound more like an ongoing or repeated process.

This is very common in Czech:

• až přijdu = when I come / when I arrive
• než odejdu = before I leave

So even though dám looks present, it refers to a future action in this kind of sentence.

Než means before in this sentence.

It introduces a subordinate clause:

• Než dám košile do pračky = Before I put the shirts in the washing machine

Czech uses než very often for this kind of time relationship.

It can also mean than in comparisons:

• je větší než já = he is bigger than me

So než has more than one use, but here it clearly means before.

Because Než dám košile do pračky is a subordinate clause, and Czech normally separates subordinate clauses with commas.

So the structure is:

• Než dám košile do pračky,
• dívám se, jestli v nich nic není.

There is also a comma before jestli for the same reason: jestli v nich nic není is another subordinate clause.

Czech punctuation with subordinate clauses is usually stricter than English punctuation.

Because košile is the accusative plural of košile.

The noun košile is feminine, and in the plural, the nominative and accusative forms are the same:

• nominative plural: košile
• accusative plural: košile

Since dát takes a direct object, košile here is in the accusative:

• dám košile do pračky = I put the shirts into the washing machine

So even though the form looks like the dictionary form, here it is functioning as plural accusative.

Because do means into / to inside of, and it requires the genitive case.

The noun is:

• pračka = washing machine

After do, it changes to genitive singular:

• do pračky = into the washing machine

This is a very common pattern:

• do školy = to school / into the school
• do auta = into the car
• do domu = into the house

So do + genitive is the key rule here.

The basic verb is dívat se, which means to look or to watch.

It is a reflexive verb, so it normally appears with se:

• dívám se = I look / I am looking

You generally cannot just remove se and keep the same meaning.
In Czech, many verbs simply belong together with se as part of the standard form.

Here dívám se means something like:

• I look
• I check
• I inspect

So the sense is: Before I put the shirts in the washing machine, I check whether there is nothing in them.

Here jestli means if / whether.

It introduces an indirect yes/no question:

• dívám se, jestli v nich nic není
  = I check whether there is nothing in them

English often uses if or whether in this kind of sentence, and Czech commonly uses jestli.

You may also see zda, which is more formal:

• dívám se, zda v nich nic není

But jestli is very common in everyday speech.

V nich means in them.

It refers back to košile (shirts). In natural usage, it often really means in the shirts, especially things like pockets.

Why nich?

Because:

• v = in
• after v, Czech uses the locative case
• the locative plural form of oni/ony here is nich

So:

• v nich = in them

Examples:

• v domě = in the house
• v autech = in the cars
• v nich = in them

Because Czech uses double negation as a normal rule.

In English, we usually say:

• there is nothing in them

In Czech, that becomes:

• nic není

Both the pronoun and the verb are negative:

• nic = nothing
• není = is not

This is standard Czech grammar, not an emphatic or nonstandard form.

Other examples:

• Nikdo nepřišel. = Nobody came.
• Nic nevidím. = I can’t see anything / I see nothing.
• Nikdy tam nechodím. = I never go there.

So if you use nic, the verb is normally negative too.

Yes, that is possible.

Both of these are natural:

• jestli v nich nic není
• jestli v nich není nic

The difference is mostly about word order and emphasis, not basic meaning.

Very roughly:

• nic není can sound slightly more neutral or flowing here
• není nic may put a bit more focus on the absence of anything

Czech word order is more flexible than English, but it is not random. Different orders can sound more natural depending on rhythm, emphasis, and context.

Most naturally, it sounds like a habitual/general action:

• Before I put shirts in the washing machine, I check whether there’s nothing in them.

Czech often uses present tense for habits and routines.
At the same time, the perfective verb dám still presents the putting-in as a single completed event each time.

So the sentence combines:

• a general habit overall
• a completed future action inside that repeated situation

This is very typical Czech aspect usage.

Because Czech has no articles.

English says:

• the shirts
• a washing machine
• the washing machine

Czech usually just says:

• košile
• pračka / pračky

The exact meaning depends on context.

So do pračky can mean:

• into the washing machine
• sometimes simply into a washing machine, depending on context

In this sentence, English would most naturally translate it with the washing machine, but Czech does not need a separate word for that.

Because není does not agree with košile here.

The subject of není is really nic:

• nic není = nothing is there

So the grammar is based on nic, not on košile.

The shirts are only part of the phrase v nich (in them), which tells you location.
They are not the subject of the verb.

That is why singular není is correct.

Yes. In natural English, I check is often the best translation here.

Word-for-word:

• dívám se = I look

But in this context, the real meaning is:

• I check whether there’s nothing in them
• I make sure there’s nothing in them

So dívám se is being used in a practical sense: looking in order to verify something.

That kind of slightly less literal translation is often the most natural way to understand Czech sentences.