You might go over how we use postures (sitting, standing kneeling, bowing, etc…) in our worship. This is because we are not pure spirits, but a body and soul composite, and when we worship, we worship with our whole selves.
I’d also go over a basic overview of the parts of the Mass (pray for God’s forgiveness in the Penitential rite, listen to readings form the Bible, sermon, creed stating what we believe, prepare for communion, consecration, communion rite, dismissal).
Finally, with regards to his not receiving communion, I’d compare it to marriage. The marital embrace is a good and holy thing, but it is reserved for those who have publically professed their union (ie, marriage vows). Just the same with receiving Holy Communion: until a person publically unites himself to the Catholic creed and is confirmed/baptized Catholic, he should refrain from receiving her sacraments. Also, assuming he does not believe in the Real Presence, it would not be honest for him to receive, for as Paul the Apostle tells us in 1Corinthians 11:29, “to eat and drink without recognizing the body and blood brings damnation unto himself.” You’re just looking out for him.