When you start a challenge, you will be prompted (in step 2) to choose between an individual and a groupschallenge.
Whereas the individual challenge concerns just yourself , the groupchallenge will enable you to add up to 24 participants to the challenge. The person raising the groupchallenge will be considered the administrator and will therefore be the sole person able to update the challenge and to close it. When creating a group-challenge a group-name needs to be added.
A challenge can only be linked to a single charity projct. Meaning that for groupchallenges all participants will raise funds for the same charity organisation.