In simple words, a team is a group of users who work together to archive a common goal, they may share tasks or responsabilites.
Since Tuqqi is a collaborative tool, this feature helps you to work not only with your tasks, also to be aware about what your team is working on.
The teams are specially usefull in the following scenarios:
In the Action Center or in the table members filters, you can quickly select the team members and do not need to do it user by user.
In the group member: if someone adds a team as group members, everytime somebody is added to the team (or removed from the team), the system will automatically update the group members and their permissions.
Assigning a team to an item: you can quickly select many team members as assignees of a specific item, regardless the datatype or status. If, for example, all the finance team is responsible for an item titled "Send the documentation to the accountant" then you can quickly select all of them
Mentioning a team: Have you ever had to mention all the members of a specific team in a comment? Now, you can do it much easier: instead of one by one, simply type the team's tag.
Consider that only admins can manage teams, you can learn about it here