If you want to edit an object, you must first select it. For most types of objects, it is sufficient to simply click on the desired object. A frame will then appear around the object to indicate that it is now selected.
Note: This does not work with text fields, text frames and other objects that have transparent fills. To select such an object, click on its border or switch to object mode (see next section), where all types of objects can be easily selected by clicking on them.
Once an object has been selected, you can no longer change the normal text, but only edit the selected object. If you want to continue working on the text, simply click with the mouse on the desired position in the text. This will deselect the object.