Once you have clicked the text box tool, your options will appear in the tool bar.
Click "Add Text Box" and this box will appear on your screen
Type in your text and you can then choose your font, style, size, text alignment, colour and background colour. Click create and you will see the text box on your plan. Drag it to the correct position with your mouse. You can also resize it by clicking the small boxes on the border.
Click Save and its complete.
To delete a text box, click the text box tool, click on the text box you wish to delete and press the delete button on your keyboard.
This video tutorial will show you how to use the Text Tool: https://vimeo.com/268531280