One-to-one communication It is the conversation you have with another person

One-to-one communication
It is the conversation you have with another person. When talking to the other person the other person needs to feel relaxed and happy to talk to you.
When start a conversation you need to start with a greeting (warm up) then exchange information (conversation) and then finish the conversation.

Group communication is a conversation between 3 or more people, but not more than 20 people.
Effective group communication is produced when there is a leader. In group communication it is important that the individuals in the group feel involved in the conversation. Non verbal communication is more important than verbal in a group conversation because it gives others a feedback and reaction. You also have to be a good listener.
It is also important to make sure that all group members can hear and see each other clearly, because that way everyone will understand and benefit from the conversation.