The form stare per + infinitive indicates an action that has not yet begun but is imminent.
- Sbrighiamoci a tornare a casa, sta per piovere!
- Let’s hurry back home, it’s about to rain!
- Stavo per fermarmi al semaforo, quando un’auto mi ha tamponato.
- I was about to stop at the traffic light when a car hit me.
This form is used almost exclusively with the present and the imperfect, rarely with the simple future, but never with compound tenses.
- Il bambino stava per uscire, quando sua mamma lo ha chiamato.
- The boy was about to leave when his mother called him.
- Mia sorella sta per tornare dalla Gran Bretagna.
- My sister is returning from Great Britain.