Editable block of text on click is available in the Editable Grid. Inline text is replaced with the editable form control.
Outside of grid you would need to wire up your own chain of event and components to accomplish the same. For example you could use a Label component or a Display Field component, add click listener and create a Window component with a textarea (or HTMLEditor) child item and a save button. On save you would run you own logic to copy input value(s) to a model class or send it back to the server via AJAX call. An example of Window popup with multiple components is demonstrated here: http://docs.sencha.com/extjs/4.2.2/#!/example/window/layout.html
Another example of inline editor is shown in this example: http://docs.sencha.com/extjs/4.2.2/#!/example/simple-widgets/editor.html It uses Ext.Editor class to turn a simple label into an editable field.
Yet another way to edit existing data (Form editor on per row basis) http://docs.sencha.com/extjs/4.2.2/#!/example/build/KitchenSink/ext-theme-neptune/#form-grid