There's no one correct answer to this question, because usage differs among faiths and sects. Reverend is usually a courtesy title for Protestant Christian ministers or pastors. It's not an official rank, it's an adjective indicating respect for the position. It's similar to saying "The Honorable Judge Forcythe" or "Your honor" in court. The judge does not have a title of "The Honorable" the title is probably Judge. The adjective is there to indicate respect, not to identify a specific job.
While it's often used as a title, it comes from use as an adjective meaning meaning worthy of respect or reverence
Some sects actually consider it inappropriate or offensive to use the title Reverend for a person, as they consider it a title reserved for God.
In Catholicism, it is usually used along with an actual title. For example, The Very Reverend Bishop Furley. Bishop is the title, Very Reverend is a way to indicate this bishop is particularly worthy of respect. A Catholic priest could be called Reverend, but could also be called Father.
You may also see "Right Reverend" used in the Episcopal and Anglican churches for bishops, and "Most Reverend" for archbishops.
A pastor is a role, a position or "job" if you wish. You could call Mr. Smith "Pastor Smith" the same way you would say "Farmer Brown" or "Doctor Jones".
A member of the clergy could be a pastor, a priest, a minister, a deacon, some other title. A deacon can be Catholicy clergy under a priest, but could also be a lay position in a Protestant church.
Generally speaking, if someone is referred to as "Reverend Smith" you can assume they are a member of the clergy, probably Protestant, but you can't be sure of their exact position or title.
As a result of this, reverend has become a noun in some cases. "Mr. Smith is the reverend at our church." This is technically not correct in most cases, though it's possible some sects could use it as an official title.
So to answer the question, it depends on the faith of the person you are introducing. There is no one correct answer to this question, you need to deal with this on a case-by-case basis.
I would start by asking the pastor what their preference is.
If that's not practical, try to use whatever title the church in question is known to use. Reverend is the adjective, pastor or minister is more the title.
"Please let me introduce Reverend Samuels, the minister of my church."
For a more formal introduction, if Samuels has a doctorate, you could say "The reverend Dr. Smith of Holy Something Church".
If you're talking to a Catholic priest, usually you call him Father.