Here's some helpful apps you can add to Teams to get started:

Planner
Help your team to stay organized, assign tasks, and keep track of your progress. Planner lets you attach files to tasks, work together on those files, and have conversations around tasks without switching between apps.
Microsoft To-Do: List, Task & Reminder
Get your lists anywhere, share lists and tasks, create color-coded lists, break your tasks into manageable steps, get notifications and sync with your calendar.
Notebook (OneNote)
Capture and share ideas, to-do lists and other thoughts with your team.
Website
The website tab lets you pin a secure website at the top of a channel or conversation so everyone has easy access to important sites.
Polly
Polly is a survey app that lets you create surveys in Teams. You can quickly create polls in your Teams channels and view results in real-time.
GitHub
The GitHub integration in Teams allows you to create and share code for your projects.
Any Microsoft Office product
Word, Excel, Powerpoint, Sharepoint... you can integrate any Office product into Teams.