why is "they carry the apples here" wrong?
NESOU suggests it is happening as we speak. If they carry apples here as part of their job every Tuesday, the Czech sentence would be NOSÍ SEM TA JABLKA.
How do you know when to use "sem" vs. "tady"?
Tady/tu/zde is a location. Sem is a direction, it was hither in older English vs. here for a location. In German sem=her, tady=hier.