1. When one meets people.
2. Enters his house, masjid, office, classroom, or any place;
3. Or leaves his relatives, friends, or any person.

Is there a reward for shaking hands when giving salam?

Al-Bara reported the Messenger of Allah said: “No two Muslims meet and shake hands, but their sins will be forgiven (by Allah) before they leave each other.” (Declared sound by Abu Dawood) (i.e. Allah forgives minor sins but major sins require sincere repentance)