CIM means cum in mouth. It’s where you ejaculate into your partner's mouth. The difference between CIM and CIM (with condom) is that you wear a condom when getting oral and when you cum. Wearing a condom stops the risk of infection making it a safer experience. To spice things up, one can always use flavored condoms as it cuts down on the latex taste.
It’s always important to be vocal too. Let your partner know how pleasurable the experience is and always tell her when you’re about to cum. She will not only thank you for it, but she’s more likely to do it again in the future.