Use the word "gentleman" when talking about a man. The plural form is "gentlemen." The pronunciation is about the same for both singular and plural forms. This word is used in formal settings, in business, and when trying to be polite.
The gentleman in the dark blue suit needs assistance with his luggage.
Please bring these drinks to the gentlemen sitting under the umbrella.
Excuse me, gentlemen. Does this jacket belong to any one of you? (addressing a group of men)
Would the gentleman at the microphone please state his name and address? (This sounds very formal. Notice the use of the third person in this case.)
Ladies and gentlemen, may I have your attention, please? (This is a very common way of addressing a large gathering of men and women.)
Rosa explained to the police officer that the gentleman in the red Ferrari cut her off at the intersection and caused her car to crash.
A gentleman always lets a lady go first. (It’s customary in the United States to allow a woman to go before a man at an entrance or exit.)
Note: Don’t address a man directly as "gentleman." That would sound strange. However, when men are gathered as a group, you can use the plural form, "gentlemen."