It's used to refer to a specific instance or occurrence, usually in contrast to previous times.
Here are some examples of how "cette fois" is used:
* Cette fois, je vais essayer de faire mieux. (This time, I'm going to try to do better.)
* J'ai compris cette fois. (I understand this time.)
* Cette fois, je ne vais pas me laisser faire. (This time, I'm not going to let myself be taken advantage of.)
It's important to note that "cette fois" is a feminine phrase, so it will agree with the gender of the noun it modifies. For example, you would say "cette fois-ci" if you were referring to a specific time that you could identify, or "cette fois-là" if you were referring to a specific time in the past.