When you belong to a space that isn't moderated, you're all members of the space with the same privileges. You can add people and remove people to the space and change the space name.
If you moderate a space, you remove other people's ability to add or remove people, edit space information, and make other people moderators. As a moderator, you can also delete other people's messages, but make sure you follow your organization's policy before you delete anything.
You can participate in a space even if you're not part of the same company. As an external participant, though, you won't be able to see or join other spaces. The administrator may keep you from changing certain space settings, but you can participate as a member of the space, sharing your expertise on one aspect of a larger project.
If you created the team, you're the team's moderator. You control which spaces are available and who belongs to them. When you add people to the team, they are automatically added to your team's home space, General.
You can also make other people on the team moderators so they can share these responsibilities with you. So, even if you haven't created the team, you might still be a moderator.
If a moderator adds you to the team, you are automatically added to a team space called General. After you become a team member, you can join other team spaces. You can also add other people as a guest to a space within a team. But only the moderator can add new people to the team.
If someone adds you to a team space without adding you to the team, you become a guest in that space. As a guest, you won't be able to see or join other spaces in the team. Your administrator may keep you from changing certain space settings, but you can participate as a member of the space, sharing your expertise on one aspect of a larger project.