Ten tools are available in the Develop module by default:

Ikona. Presets;
Ikona. Quick Fix;
Camera and Lens;
  Crop and Rotate;
Gradient Filter;
Radial Filter;
Filter Brush;
Smoothing Brush;
Retouching Tools.

Additionally, tools for work with documents can also be added into the Develop module’s controls:

Ikona. Highlighter;
Ikona. Anonymization;
Ikona. Annotation.

To add the tools for work with documents, use their option in the Preferences. Press Ctrl+M to show the Preferences. Then go to the “Other” preferences and turn on Show tools for work with documents in Develop.

All the tools are shown in the right panel, underneath individual icons. Other than the Presets, all the tools are also available under Tools in the top menu. Activating a tool opens it in the right panel and shows its functions and settings.

If you have already used a function or setting to adjust the current picture, an indicator—a blue dot—is shown next to the given tool’s icon in the right panel.

The various tools are shown in the top toolbar. Clicking a tool displays that tool’s settings. Clicking it again hides these settings. The configured settings are used automatically when the tool is applied. All of the tools can be restored to their default settings. To restore a tool to its default settings, click the arrow icon in that tool’s header. Click Close or press Esc to switch to the magnifying-glass tool.

If the tool works with a mask, then a mask list is shown towards the top of the Side Panel. Click an item to set a mask to work with. To add a new mask, click Add Mask. To Delete a mask at any time, click the button with the trash-can icon to the right of the mask list or in the right-click menu for a mask. That menu also contains items to Rename or Duplicate a mask. Use the checkbox next to a mask’s name to disable or re-enable it. Hover the mouse over a mask’s name to temporarily highlight the mask in blue in the picture. To display a mask permanently, use the Mask button at the top of the panel.