Currently, there are 4 different roles in tribe communities: Member, Admin, Moderator, Bot. Each role has different level of accessibility, and only admins are able to change the role28 of the user's account. Here are the difference between these roles.
Members are end users who are part of the community and can post content and comment, up-vote other's answers, and manage their-own account.
Admins have full access to community settings, theme, apps and integration, analytics, users and content export. They can delete accounts from the community, changing the links and look and feel, and many more accessibilities in the admin panel.
Moderators have access to moderate the content and ban users.They can edit the contents and make sure that the posts are qualified and appropriate. They have no access to the settings of the community. Find more information in here: What are the roles and responsibilities of a community moderator?44
Group Admin: (Can only be assigned within a group)
The group admin can only manage the settings related to the group they are assigned to. That includes changing the role of other group admins and group moderator, changing the posts, adding or removing members, changing the group type and other group settings.
Group Moderator: (Can only be assigned within a group)
The group moderators can only moderate the content and members within that particular group. This includes modifying posts, adding or removing members and managing join requests if the group is private or secret.
Bot is a fake account under the control of the admins. A bot is an unreal profile designed to act like a real member and to interact with the other users. Community admins/moderators can use the face of bot accounts for posting content and up-voting others' answers. The purpose is to build an engaging environment and to encourage all the members to interact with each other. To learn more about the bot users, click on this 44and this35 link.