Some introductions are required for certain occasions, especially when two strangers meet in the company of a mutual friend. Whenever this situation occurs, an introduction is in order.
It is rude of one who knows the other two, to chat with one and leave the other-unacknowledged and left out-standing by as if they do not exist ( for me personally if they don't have any conversation, I just let them be). Rules of introduction have become more relaxed over the years, but certain forms should be followed in professional settings.
One person is always introduced to another, achieved in two ways. One, by actual use of the word "to", for example, "Mr. Knowles, I'd like you to introduce you to Mrs. Sampson." Secondly, (most generally used) is by saying the name of the person to whom the other is being introduced ( I personally am bad with names), without using the preposition "to", but instead "may I introduce Mr. Knowles."
Three basic rule:
Fitness and Health