Přesazování začíná výběrem květináče.

Přesazování is a verbal noun: a noun made from a verb. It means repotting / transplanting as an activity or process.

• base verb: přesazovat = to repot, to transplant
• noun: přesazování = repotting, transplanting

In this sentence, it is the subject of the sentence, and it is in the nominative singular. So the structure is basically:

Repotting begins ...

It is also a neuter noun.

Both forms exist, but they have slightly different feel.

• přesazování is connected with the imperfective verb and usually refers to the process or activity in general
• přesazení is connected with the perfective verb and more often refers to one completed act

In an instructional or general statement like this, přesazování sounds natural because the sentence is talking about the whole procedure of repotting, not just one finished event.

Because the subject přesazování is singular.

Začíná is the 3rd person singular present tense of začínat = to begin / to start.

So:

• přesazování začíná = repotting begins
• not začínají, because that would be plural

Even though the English translation may sound a bit more natural as Repotting starts with..., Czech is simply agreeing the verb with the singular noun přesazování.

Because Czech uses the pattern začínat něčím = to begin with something.

So after začínat, the thing you begin with is often in the instrumental case:

• výběr = selection, choice
• výběrem = by/with the selection, with choosing

So začíná výběrem literally means something like:

begins with the selection

This is why Czech does not need a separate word matching English with here. The case ending itself carries that function.

Because výběr often takes the genitive to show what is being selected.

The pattern is:

• výběr něčeho = selection of something

So:

• květináč = flowerpot / plant pot
• květináče = of a flowerpot / of the flowerpot

That means:

• výběr květináče = the selection of a flowerpot
• more naturally in English: choosing a flowerpot

So the sentence contains two linked case patterns:

• začíná výběrem → instrumental after začínat
• výběrem květináče → genitive after výběr

Because Czech is using a noun phrase, not a verb phrase.

Compare these:

• vybrat květináč = to choose a flowerpot
  
  • here květináč is the direct object, so it is accusative
• výběr květináče = the choice/selection of a flowerpot
  
  • here květináče depends on the noun výběr, so it is genitive

So English uses a verb very naturally, but Czech here uses a noun: not choosing a pot as a verb form, but literally the selection of a pot.

Because Czech has no articles.

So květináče could mean:

• a flowerpot
• the flowerpot

The exact meaning depends on context. In a general instructional sentence like this, English usually says a flowerpot or the right flowerpot, but Czech leaves that unspecified unless something in the context makes it clear.

Yes. Czech word order is fairly flexible because the case endings show the grammatical relationships.

The given sentence is a neutral, natural way to say it:

Přesazování začíná výběrem květináče.

But you could also change the order for emphasis, for example:

Výběrem květináče začíná přesazování.

That puts more focus on výběrem květináče.

So the meaning stays basically the same, but the emphasis shifts.

A few useful pronunciation points:

• Czech stress is usually on the first syllable of each word:

  • PŘEsazování
  • ZAčíná
  • VÝběrem
  • KVĚtináče

• á and í are long vowels

• č sounds like ch in church

• ř is a famous Czech sound with no exact English equivalent; a rough approximation is something between r and zh

Very roughly, for an English speaker:

• přesazování ≈ przhe-sa-ZO-vaa-nee
• květináče ≈ KVYE-ti-naa-che

Those are only approximations, but they can help you get started.