Při otočce jsem šlápl na botu.

After při, Czech normally uses the locative case.

So:

• otočka = basic dictionary form (nominative)
• při otočce = locative singular

Here při means something like during, while doing, or in the course of.

So při otočce is literally something like:

• during a turn
• while turning

A useful pattern is:

• při práci = during work / while working
• při cestě = during the trip / on the way
• při otáčce / při otočce = during a turn / while turning

Otočka comes from the idea of turning or making a turn.

Depending on context, it can mean things like:

• a turn of the body
• a quick turnaround
• a turning movement
• in some situations, even a U-turn

In Při otočce jsem šlápl na botu, it most naturally means something like while turning around or during the turn.

So this is not necessarily a formal traffic U-turn. It is more likely a physical turning movement.

This is the Czech past tense.

Czech past tense is usually formed with:

• a past participle
• plus a form of být (to be)

Here:

• jsem = I am / I have-type auxiliary used in the past tense
• šlápl = past participle of šlápnout

So:

• já jsem šlápl = I stepped

In normal Czech, the subject pronoun já is often omitted, so just jsem šlápl is enough.

Also notice the ending:

• šlápl = masculine speaker
• šlápla = feminine speaker

So a woman would usually say:

• Při otočce jsem šlápla na botu.

Šlápl is the past form of šlápnout.

That verb means:

• to step on
• to tread on
• sometimes more generally to put one’s foot down onto something

A related imperfective verb is šlapat.

The difference is mainly aspect:

• šlápnout = perfective, one completed step
• šlapat = imperfective, repeated action, ongoing action, or habitual stepping

Here the perfective verb is natural, because the sentence describes one single completed event: the speaker stepped on a shoe once.

Because with šlápnout na, Czech uses the accusative.

So:

• bota = shoe
• na botu = onto the shoe / on the shoe as the target of the step

This is a very common Czech pattern:

• šlápnout na nohu = to step on someone’s foot
• šlápnout na brzdu = to step on the brake
• šlápnout na botu = to step on a shoe

Why not na botě?

• na botě is locative
• it usually means on the shoe as a location, not the object affected by the step

So in this sentence, na botu is the normal form.

Czech often leaves out possessive words if the meaning is clear from context.

So na botu can mean:

• on a shoe
• on someone’s shoe
• on his/her/my shoe

English often wants this to be more explicit, but Czech does not always need it.

If needed, Czech could say:

• na mou botu = on my shoe
• na jeho botu = on his shoe
• na její botu = on her shoe

But without a possessive, the sentence is still perfectly natural.

Because Czech often drops subject pronouns when they are not needed.

In English, you must say I stepped.

In Czech, jsem šlápl already shows the person clearly enough in normal usage, so já is usually omitted.

You can add já for emphasis:

• Já jsem šlápl na botu.

That sounds more like:

• I stepped on the shoe.
• It was me who stepped on it.

But in a neutral sentence, leaving out já is standard.

Yes, that is possible.

Both šlápnout na and stoupnout na can mean to step on.

Very roughly:

• šlápnout na often feels a bit more direct, physical, and common in everyday speech
• stoupnout na is also very common and natural

In many situations, they are interchangeable.

So both of these can work:

• Při otočce jsem šlápl na botu.
• Při otočce jsem stoupl na botu.

The first one may feel slightly more vivid.

They are close, but not exactly identical.

• Při otočce = during the turn / while turning
• když jsem se otočil = when I turned around / when I had turned around

So při otočce focuses on the action as it was happening. Když jsem se otočil sounds more like a full clause with a time point.

Compare:

• Při otočce jsem šlápl na botu.
  While turning, I stepped on a shoe.

• Když jsem se otočil, šlápl jsem na botu.
  When I turned around, I stepped on a shoe.

Both are possible, but the original sentence is a bit more compact.

Yes, it is natural.

It sounds like a normal way to describe an accidental action in the past.

A few close alternatives would also be natural, for example:

• Při otočce jsem šlápl někomu na botu. = I stepped on someone’s shoe while turning.
• Když jsem se otáčel, šlápl jsem na botu. = While I was turning, I stepped on a shoe.
• Při otáčení jsem šlápl na botu. = While turning, I stepped on a shoe.

The original sentence is concise and idiomatic.

A very useful pattern here is:

• Při + locative for during / while
• past tense with jsem + past participle
• šlápnout na + accusative

So you can build similar sentences like:

• Při běhu jsem šlápl na kámen.
  While running, I stepped on a stone.

• Při tanci jsem jí šlápl na nohu.
  While dancing, I stepped on her foot.

• Při vystupování z autobusu jsem šlápl do kaluže.
  While getting off the bus, I stepped into a puddle.

The main things to remember are:

1. při takes the locative
2. šlápnout is perfective and good for one completed step
3. na here is followed by the accusative