It is the default view of the user interface. This will list down all the DAGS present in your system. It will give you a summarized view of the DAGS like how many times a particular DAG was run successfully, how many times it failed, the last execution time, and some other useful links.
In the graph view, you can visualize each and every step of your workflow with their dependencies and their current status. You can check the current status with different color codes.
The tree view also represents the DAG. If you think your pipeline took a longer time to execute than expected then you can check which part is taking a long time to execute and then you can work on it.
You can access logs of the individual tasks run in Airflow UI which will help to learn more or troubleshoot an issue