Right now, your community members (non-admins) are able to create only one type of topics which is tag. While, your community management team can create two other topic types (Category and Collection) which both have more value that Tags. To learn more about the difference between topic types, please check out this answer4.
However, this worths mentioning that we have plans to change the structure of topic on our product. We are going to unify all these 3 different topic types and we will make it possible to let the community admins to choose if they want their regular members to be able to create topics or not. We will share more information on our community fro public later on. We will also send a message to all our community admins once the changes are coming soon. We cannot share any deadlines with our basic (free version) clients.