Jobs and tasks have various properties that are all editable. To edit properties in the main window, double click on the field you want to edit. For example, double clicking on a Job's title will allow you to type in a new name, while double clicking the date of a task will bring up a small date chooser window, letting you select a new date. For the latter example, simply click outside the date chooser window to cause it to disappear.
These properties, and additional ones not visible in the main window, are also editable by using the Info panel. This window can be made visible by clicking the Info icon at the top of the main window or by choosing "Info Panel" from the "View" menu. The contents of this window will change based on which item you have selected in the main window. Click on the job or task you are interested it to edit its settings. Jobs contain extra info such as Hourly Rate and Invoice number that will appear when creating an invoice for that particular job.