If the words can't be seen in some modules it is likely to be because it is a dictation module, which relies on the auditory element to reinforce learning. Every 5th module is set as a dictation module and it is possible to turn on dictation in other modules too.
Press and hold number 5 on the keyboard to temporarily view the word.
If a dictation module is too challenging, you can turn the feature off.
To turn off a dictation module:
Locate the TTRS Course menu
Click the DICT icon to turn off the dictation feature on that module