There's a specific time range for mass, ranging from 4 PM on Saturday until….can't remember the other time but late on Sunday. So going to mass at 7 AM on Saturday does not fill your weekly mass quota. Skipping it is frowned upon, but it isn't necessarily a mortal sin. Weekly mass is very encouraged, as well as mandatory mass on holy days of obligation, such as Christmas, the Immaculate Conception, the Epiphany, and All Saints Day, to name a few.
There's seven sacraments, which will be basically drilled into your memory in any religious ed classes you take. If your character goes to public school, they'll almost definitely be taking a religious ed class once a week to learn about the faith and to prepare for upcoming sacraments. If they were born and raised Catholic, they were likely baptized a month or so after birth.
A few years after (usually winter of second grade) is First Reconciliation, which is part of the preparation for First Communion since it's the first time they confess their sins and do penance (confession will become a usually at least yearly thing from that point forward). Then in the spring of their second grade year is their First Communion, which is arguably the biggest one. It's when they're first allowed to receive communion at mass. Since Catholics believe that the host and wine are transformed into the body and blood of Jesus, this is a very big deal, hence the little suits and frilly white dresses involved.
Confirmation then comes when they're around fourteen. If I recall correctly, the age for confirmation was lowered a few years back from 12th grade to 9th grade or something, I was confirmed in 9th grade. You're anointed with special oils and basically officially admitted into the church, plus you take on the name of a saint to gain their protection and guidance.
If a person is not raised Catholic, they receive baptism, confirmation, and first communion all at once after a year of learning about the faith during the Easter Vigil mass, which is why it's so long.
Anointing of the Sick is another sacrament, and it's usually administered when someone is dangerously ill/in risk of dying. One time I popped into mass at a church (my sister had a volleyball game at their school) and ended up receiving it since the priest was giving it for everyone; I was in a pretty bad place so I guess you could argue that I was at risk of death? And it actually really did help my mental health for a month or so.
Then there's Holy Orders and Matrimony, and you can only get one. Matrimony is marriage, Holy Orders is becoming a priest, nun, etc. and then there's also the consecrated single life, which I have yet to meet anyone who's actually done.