Formal:
* Je l'embrasse. (I kiss him/her/it) - This is the most formal way to say it.
Informal:
* Je l'embrasse. (I kiss him/her/it) - This is also informal, but less so than the following options.
* Je lui fais la bise. (I kiss him/her on the cheek) - This is a common way to say "I kiss" in informal settings, referring to the cheek kiss that is customary in French culture.
* Je lui fais un bisou. (I give him/her a kiss) - This is a more general way to say "I kiss" in an informal context.
It's important to note that the most appropriate way to say "I kiss" depends on the specific context and your relationship with the person you are speaking to.