Kiedy jadę za szybko, instruktorka mówi, że prędkość jest zbyt duża.

Not exactly. Jadę is from jechać, which broadly means to go / travel by vehicle.

So depending on context, jadę can mean:

• I’m driving
• I’m going by car
• I’m riding
• I’m travelling

In this sentence, because there is a driving instructor, the natural English meaning is I drive / I’m driving.

This is a very common question, because Polish has a special distinction in motion verbs.

• jechać / jadę = going in one direction, on one trip, at a given moment
• jeździć / jeżdżę = going/driving habitually, repeatedly, or in various directions

So Kiedy jadę za szybko sounds like when I’m driving too fast or when I drive too fast on a given occasion.

If you said Kiedy jeżdżę za szybko, it would sound more like when I have the habit of driving too fast.

Polish often leaves out subject pronouns, because the verb ending already tells you who is doing the action.

• jadę already means I am driving
• mówi already means he/she says

So ja is unnecessary unless you want emphasis or contrast.

For example:

• Kiedy jadę za szybko... = neutral
• Kiedy ja jadę za szybko... = emphasis, something like when I’m the one driving too fast...

It can be understood as either, depending on context.

In this sentence, because both verbs are in the present tense, kiedy often has a repeated, general meaning:

• when
• whenever

So the sentence can naturally mean:

• When I drive too fast, the instructor says...
• Whenever I drive too fast, the instructor says...

Polish often uses the present tense like this for repeated situations.

Yes. Gdy can also mean when.

• kiedy is very common and neutral
• gdy is also correct, but can sound a bit more formal or written depending on context

So Gdy jadę za szybko, instruktorka mówi... is grammatical and natural too.

Because instruktorka is the feminine form, meaning female instructor.

• instruktor = male instructor
• instruktorka = female instructor

The ending -ka is a common way to form feminine profession nouns in Polish.

So this sentence tells you the instructor is a woman.

Yes, zbyt szybko is possible, but za szybko is more natural in everyday speech.

Both mean too fast, but there is a slight difference in feel:

• za szybko = very common, conversational
• zbyt szybko = a bit more formal or neutral

So:

• jadę za szybko = very natural spoken Polish
• jadę zbyt szybko = also correct, but less conversational

Because że introduces a full clause, like English that.

• mówi, że... = says that...

So:

• instruktorka mówi, że prędkość jest zbyt duża means
• the instructor says that the speed is too high

Unlike English, where that is often omitted, Polish usually keeps że in sentences like this.

For the speed of a vehicle, prędkość is the normal word.

In driving and road contexts, Polish usually uses:

• prędkość samochodu
• ograniczenie prędkości
• mierzyć prędkość

Szybkość exists too, but it is less natural here. It is broader and often feels more abstract, technical, or connected with quickness rather than standard road-speed wording.

So in this sentence, prędkość is the expected choice.

Because in Polish, speed is usually described as large/high, not fast.

Natural Polish phrases are:

• duża prędkość
• wysoka prędkość

But szybka prędkość sounds unnatural.

So prędkość jest zbyt duża means the speed is excessive.

Also, duża matches prędkość grammatically:

• prędkość is feminine singular
• so the adjective is also feminine singular: duża

A more conversational version could also be:

• prędkość jest za duża

That is also correct. zbyt duża just sounds a bit more neutral or formal.

Because Polish requires commas around subordinate clauses.

There are two of them here:

• Kiedy jadę za szybko,
  The comma separates the when clause from the main clause.

• instruktorka mówi, że prędkość jest zbyt duża
  There is a comma before że, because że prędkość jest zbyt duża is another subordinate clause.

So both commas are standard and required in Polish spelling.