The other translation given is "I step up in the school". That is the literal translation, yes... that doesn't actually, like mean anything that anyone would understand if you said to them...

(Furthermore, in English we'd say "at the school", unless you specifically want to stress that the performing is taking place within the building, and not, say, outside in front of it)

Idiomatic expressions should have their own section.

The origin of this expression might be German: "auftreten" -> up/onto + step which translates to "perform" if it is without a direct object

I think of it like "step up to the microphone", which is what you'd do if you were performing. My own mnemonic.