Learn Farsi: وقتی که سفالگر کار می‌کند، چرخ می‌چرخد.

Just like the conjunction تا (until) when it describes a factual outcome, وقتی که (when) states a fact or a recurring action rather than a wish, doubt, or condition. Because of this, it takes the indicative tense instead of the subjunctive. Here, both کار می‌کند (works) and می‌چرخد (spins) are regular present indicative verbs describing a general truth.

Is the word سفالگر (potter) made up of two parts?

Yes! It comes from سفال (clay or pottery) plus the suffix -گر (-gar). In Farsi, adding -گر to a noun often creates a word for a profession or someone who works with that thing, much like the '-er' ending in English. So, a سفالگر is a pottery worker or potter.

I noticed چرخ (wheel) looks very similar to the verb می‌چرخد (spins). Are they related?

Absolutely. چرخ (wheel) is a noun related to the verb چرخیدن (to spin or to turn). In Farsi, it is very common for objects to share the same root as the action they perform. The verb می‌چرخد is the present indicative 'it spins', built on the present stem of that same root.

Could I just say وقتی instead of وقتی که?

Yes, you can drop the که in everyday conversation, and people frequently do. Both وقتی and وقتی که mean 'when' as a conjunction linking two clauses, but keeping the can sound just a little bit more formal or complete in writing.