If you are the link between people who have never met it is up to you to make the introductions. Remember the hierarchy: men should be introduced to women, juniors to elder people and higher ranks. Introduce individuals to the group first and then the group to the individual. For example, 'Mary, this is Jim, Bob and Sue. Everyone, this is Mary.'
Unless the occasion is formal there's no need to mention surnames. If possible, offering a little information about each person as you introduce them ('Rupert and I were at school together') will help to break the ice.
The traditional British greeting on introduction is 'How do you do?'. The appropriate response - however strange it may seem - is to reiterate the phrase 'How do you do?'. In situations where this exchange may seem too formal, a friendly 'Hello' will usually do.
At an even more informal level, if someone says 'Hi, how are you?' or 'Hi, how's things?' - the response should be positive and upbeat: 'Fine thanks, and you?'' or 'Fine thanks, can't complain'.