Allow me to post a previous post of mine on this issue:
My wife presented a beginning apologetics bible study for her women’s group which was very well received. We worked on it together and here’s the topics we covered:
Apologetics 101: What Do Catholics Believe and Why?
Week 1: Sola Scriptura? (The Bible Alone?)
Where did we get the Bible? What is the role of the Bible in the Church? What is Sacred Tradition?
Week 2: Salvation – How do we get to heaven?
Do Catholics really believe we can work our way to heaven? Can we lose our salvation?
Week 3: The Sacraments
What are sacraments? Why are they necessary? Why do we baptize infants? Why do we believe in the Eucharist?
Week 4: The Pope, the Bishops and the Magisterium
Where does the pope get his authority? Why do we have a church hierarchy? When does the pope speak infallibly? What exactly is “Church teaching?”
Week 5: Mary and the Marian Doctrines
Do Catholics worship Mary? Does she have a role in salvation? What about the Marian Doctrines (The Immaculate Conception, The Assumption) and Marian apparitions (Lourdes, Fatima, etc)?
Week 6: Communion of Saints
What do Catholics believe about the saints? Why do we pray to them?
Week 7: Tour of the Church/The Meaning of Catholic Practices
What is the meaning of the various items in the church? Why do we have statues, paintings, icons, holy water, incense, candles, etc? Why do we have a crucifix instead of just a cross?
Why do Catholics cross themselves? Why do they kneel, stand and sit at various times of the mass?
What are relics, scapulars and medals?
Week 8: The Last Things – Heaven, Hell, Purgatory and the End Times
Do Catholics still believe in Purgatory? Why? What do we know about heaven and hell? What is “Limbo”? What do we believe about the end times?
In our experience, you cannot assume your audience, even lifelong Catholics, have any working knowledge of apologetics, the Scriptures, and an adult level knowledge of Catholic teaching. Be prepared to explain the basics.
You also might want to check these previous threads for more ideas: