To add a tool click on the green plus icon
at the bottom of either of the side panels.
You will be shown a list of all of the tools that are not currently visible.
Select one of them for it to be added to the bottom of the relevant panel.
To remove one of the side panel tools, right-click on it. You will be shown a dialog with the option to remove it from the panel along with any other options available for the tool.
You can move tools by removing them and re-adding them in the order you would like. We do plan to implement a drag and drop interface to make this easier!