Liturgical days are either feasts days or days in a particular season (Advent, Christmas, Lent, Easter, Ordinary Time).
Feast days are divided into 4 types: Solemnities, Feasts, Memorials, Optional Memorials
Days in seasons are of two types: Sundays and weekdays (feriae)
To arrange the calendar, first look to see if it is a saint’s day, and if so, what is the rank. Then look at which day in which season it is (e.g. Wednesday after the Third Sunday of Lent). Then use the table found
here, to see which one is higher. That’s the one you use for that day.
If the omitted day is a Solemnity, then it gets tranferred to the next day (the next day that is not a Solemnity, Feast, Sunday, Holy Week, Ash Wedneday, All Souls)
Optional Memorials are just what the name implies - optional - so you can choose to observe either the saint, or the weekday
You can also use the calendar at
universalis.org which will tell you the day; likewise, there are “Ordos” -small booklets giving which day it is, which Mass may be said, and what to recite from the Liturgy of the Hours.
Once you’ve determined the day, then follow the
General Instruction, numbers 225-240 to know where you should take a certain part from.
Feel free to ask more questions - this is not the most illuminating of answers, I know.
