Technik zapojí pračku.

Because it is the direct object of the verb, so it has to be in the accusative case.

• pračka = nominative singular
• pračku = accusative singular

This is a regular pattern for many feminine nouns ending in -a:

• žena → ženu
• firma → firmu
• pračka → pračku

So Technik zapojí pračku uses pračku because the washing machine is the thing being connected.

technik is nominative singular, because it is the subject of the sentence.

It is also a masculine animate noun. That matters in Czech grammar, especially with adjectives and in some plural forms.

Here, it is simply the person doing the action:

• technik = the technician
• zapojí = will connect
• pračku = the washing machine

Because zapojit is a perfective verb.

In Czech, perfective verbs do not normally express a true present action. Their “present” forms usually refer to a future completed action.

So:

• zapojí = he/she will connect / hook up not
• he/she is connecting

If you want an ongoing present action, Czech uses the imperfective verb:

• zapojuje = is connecting / connects

This aspect difference is one of the most important things for English speakers to learn in Czech.

It comes from the infinitive zapojit.

This is the 3rd person singular form:

• já zapojím
• ty zapojíš
• on/ona/ono zapojí

So technik zapojí means the technician will connect.

Czech normally has no articles.

So technik can mean:

• a technician
• the technician

And pračku can mean:

• a washing machine
• the washing machine

Which one is meant depends on the context. English requires articles, but Czech usually does not.

Yes. Czech word order is fairly flexible because the cases show what each noun is doing.

The most neutral order here is:

• Technik zapojí pračku.

But you could also say:

• Pračku zapojí technik.

Both mean basically the same thing, but the emphasis changes.

• Technik zapojí pračku. = neutral statement
• Pračku zapojí technik. = emphasis on the washing machine or on who will do it

So word order in Czech often affects focus more than basic meaning.

A rough guide:

• technik → TECH-nik
  • the ch is one Czech sound, like the sound in Scottish loch or German Bach
• zapojí → ZA-po-yee
  • stress is on the first syllable
  • the final í is long
• pračku → stress on PRA
  • č sounds like ch in church

A useful general rule: Czech stress is almost always on the first syllable of the word.

It can mean connect, hook up, or plug in, depending on context.

With an appliance like pračka, it usually means something like:

• connect it properly
• hook it up
• plug it in
• set it up so it can work

It does not always mean simply switch on.
For switch on / turn on, Czech often uses zapnout instead.

So in this sentence, zapojí pračku most naturally suggests that the technician will connect/install/hook up the washing machine.