When Oktopus is opened, the Sidebar will show the Standard Tools toolset by default.
To change toolsets, click the current toolset title at the bottom of the Sidebar, and select from the list that appears.
You can disable / enable toolsets by clicking the toolset title when in Aerial Mode (see Resize Tab and Aerial View).
To start using a tool, tap or click it once to activate.
Some tools are available in multiple locations if they are relevant to more than one subject area. For example, the Measurement Tools found under the Math toolset are also located under the Science toolset. In addition, the Cursor Tool and Pen Tool from the Standard Tools are available all the top of the list for all subject toolsets.
Hint: Consider adding frequently used tools to the Quick Tool Palette if toolsets are switched between often for specific tools.