“What does a priest do all day”? Firstly, it depends on the diocese: one diocese may have special programs that involve their clergy. It also depends on the priest: some priests are in different ministries. There are university-chaplains, hospital-chaplains, police-chaplains, parish-priests, Religious-priests, and monastic-priests.
For your average parish priest, the answer is often simple. I am blessed to have known my closest friend before and after his ordination, and his life has changed drastically. He took over a joined-parish, with two different church buildings separated by a mile or so. He lives in one rectory and works in the other. I work in the “working rectory” with him on weekdays, so I can say with 100% accuracy what he “does all day”:
4 AM: he wakes up at Living Rectory. Exercise. Shower. Prayers. Emails.
8 AM: he walks to Working Rectory.
9 AM: he celebrates Mass at the Working Church.
9:40 AM: begins proper office work. Often leaves for hospital visits, anointing the sick, funerals, diocesan events.
12 PM: walks to Living Rectory for lunch.
2 PM: back at the Working Rectory for meetings, spiritual direction, counseling.
4-5 PM: walks back to the Living Rectory for evening prayer.
6 PM: supper.
7 PM: varies. painting, renovating, meetings, finance councils, parish councils. visits.
9-10 PM: Sleep.
He is extremely busy and alone in his job. He never stops serving those entrusted to him. It’s not even a very busy parish, either. Boggles my mind.
The “Office Administrator” (Secretary) is a lay woman. Another administrator is a Religious Sister. Another administrator is a lay woman. Along with many laity, these people do the bulk of administration. My friend mostly manages sacramental things - but not exclusively.