Ella in Italian is an old-fashioned or formal way to say she. It is used primarily in literary or formal contexts, though in everyday conversation it has largely been replaced by lei, which is the more commonly used word for she or her.
Here are a couple of examples using ella in sentences:
Ella cammina nel parco ogni mattina – She walks in the park every morning.
Non so se ella sarà presente alla riunione – I don’t know if she will be present at the meeting.
In modern spoken Italian, using ella might sound overly formal or archaic. It’s much more common to hear:
Lei cammina nel parco ogni mattina – She walks in the park every morning.