Three resources, from the most basic to the most comprehensive, may be helpful:
From the Baltimore Catechism:
234. What is the third commandment of God?
The third commandment of God is: *Remember thou keep holy the Lord’s day.
And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had done.* (Genesis 2:2)
235. Why does the Church command us to keep Sunday as the Lord’s day?
The Church commands us to keep Sunday as the Lord’s day, because on Sunday Christ rose from the dead, and on Sunday the Holy Ghost descended upon the apostles.
**236. ** What are we commanded by the third commandment?
By the third commandment we are commanded to worship God in a special manner on Sunday, the Lord’s day.
Keep you my sabbath; for it is holy unto you. (Exodus 31:14)
237. How does the Church command us to worship God on Sunday?
The Church commands us to worship God on Sunday by assisting at the Holy Sacrifice of the Mass.
238. What is forbidden by the third commandment of God?
By the third commandment of God all unnecessary servile work on Sunday is forbidden.
Six days shall you do work; in the seventh day is the sabbath, the rest holy to the Lord. (Exodus 31:15)
239. What is servile work?
Servile work is that which requires labor of body rather than of mind.
240. When is servile work allowed on Sunday?
Servile work is allowed on Sunday when the honor of God, our own need, or that of our neighbor requires it.
From the Catechism of the Catholic Church:
**A day of grace and rest from work **
2184 Just as God “rested on the seventh day from all his work which he had done,” human life has a rhythm of work and rest. The institution of the Lord’s Day helps everyone enjoy adequate rest and leisure to cultivate their familial, cultural, social, and religious lives.
2185 On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord’s Day, the performance of the works of mercy, and the appropriate relaxation of mind and body. Family needs or important social service can legitimately excuse from the obligation of Sunday rest. The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health.
The charity of truth seeks holy leisure- the necessity of charity accepts just work.
**2186 ** Those Christians who have leisure should be mindful of their brethren who have the same needs and the same rights, yet cannot rest from work because of poverty and misery. Sunday is traditionally consecrated by Christian piety to good works and humble service of the sick, the infirm, and the elderly. Christians will also sanctify Sunday by devoting time and care to their families and relatives, often difficult to do on other days of the week. Sunday is a time for reflection, silence, cultivation of the mind, and meditation which furthers the growth of the Christian interior life.
Finally, JPII’s pastoral letter, Dies Domini: