Each tool has a tooltip to know its use when the shortcuts to use it.
1. Main tools
Main tools composed of tools to select, move, create objects, transform, … All useful information about the tool is located on its tooltip.
2. Sub tools
Sub tools depending of the main tool and selected object.
Zoom input, you can click on the icon to reset to 100%.
4. View buttons
Buttons to toggle some display as axes, grid, …
These properties can be managed in settings tab in right panel.