Tools are used for many things such as manipulating and selecting items. Most tools work using the 3D View and the Image View. To select the current tool, you can either use the widget Tools and click on the tool icon or select one through the Tools menu. Please note that there can only be one active tool in the application.
Tools always display a comprehensive contextual help describing their use, actions and shortcuts in the HUD of the 3D View or Image View. Make sure to display the HUD when you want to access to a quick help related to the currently selected tool.
Here we see the description of the Select tool on the HUD
Tools always have options. Tool options can be accessed through Tool Options widget found in Window > Tool Options... or by double-clicking on a tool icon in the toolbar.
Displaying Translate Item options
Tools dedicated to selection and picking have a special option to deal with transparency. This attribute, called Opacity Threshold, is set to 50% by default. By default, Tools consider items that are over than 50% transparent as not selectable.
A typical example where 3 transparent quads are in front of the sphere.
To change the opacity threshold of the currently selected tools, go to Window > Tools Options... and change the value of Opacity Threshold. When set to 100%, transparent items are invisible to selection whereas set to 0% transparent items are always selectable.