To select text, simply click on it. Attention: To select it, it is imperative that the layer where it is is in Edition.
To switch from input mode to section mode, click the top bar of the text selection. When text is in edition, the top bar is gray. When the text is in the section mode, the top bar is blue.
If the text is in edition mode (gray bar), the selection is done as in any text box. Simply click the mouse to the location where insert text. To enter text, simply type on the keyboard.