This article by Light House Trails Research (Click here to read) explains the difference between the Lord's Supper and the Roman Catholic mass in the context of a report on the Roman Catholic Church's current evangelistic efforts to reach unbelievers and separated brethren, which are all those who are not part of the Roman Catholic Church.
It's important that we know the difference, and not fall into C.S. Lewis' serious misconception that Communion, Mass, the Lord's Supper, are all terms used to describe the same thing:
There are three things that spread the Christ life to us: baptism, belief, and that mysterious action which different Christians call by different names— Holy Communion, the Mass, the Lord’s Supper. At least, those are the three ordinary methods.
(C. S. Lewis in Mere Christianity, Kindle location 1123)
Note that Lewis, even as an Anglican, believed the Roman Catholic doctrine of sacramental communion, which taught that by participating in the Mass one receives "the Christ life". In fact, the Mass is a religious service in which an idol (the host) is set up in front of the congregation to represent Christ (Rome says it is in fact Christ Himself!), and everyone is invited to worship it.
But the Bible says, "flee from idolatry" (1 Cor. 10:14), and "What communion hath light with darkness? And what concord hath Christ with Belial? or what part hath he that believeth with an infidel? And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people. Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty" (2 Cor. 6:14-18).
Friends, love God and keep Christ's commandments. And love the Roman Catholics, and share Christ's truth with them!