The red-framed area is the toolbar.
Here, you can manage everything related to tools.

Switch between tools
Add tools
Change brush size

Switch between tools

Simply tap the tool icon in the tool panel to switch to a different tool.

When you switch tools, the panel changes, giving you access to settings like brush size for the selected tool.

Add tools

You can add your tools of choice to the toolbar by following these steps.

1. Tap the + icon at the bottom left of the toolbar.
2. Choose the tool you want and tap Add at the top right.
   
3. The tool will be added to the toolbar.

You can also group multiple tools into a tool set.

1. Tap the + icon at the bottom left of the toolbar.
2. Select the tools you want to group together and tap Add at the top right.
3. The tool set will be added to the toolbar.

You can also add tools to an existing toolbar item to create a tool set.

1. Tap the tool you want to add others to.
2. In the popover, tap the + icon.
3. Select the tools you want to include and tap Add at the top right. You can choose more than one tool to add at once.
4. The tools you selected will be grouped as a tool set.

Change brush size in the toolbar

To change the brush size, drag your finger or stylus up and down over the brush size indicator in the toolbar.