Okay, I should have read that more carefully. Creating groups solved my problem.
Thanks.

Guys, I'm just discovering the plugins and how they can help me on improving my drawings, that's why i've installed the OS Coolean plugin. I can see the toolbar I can togle from one icone to an othe but I can't perform any fit or trim in my model. I've creted the same base exemple then we can see on youtube, but no selection possible. Yes I made two individual components to test it. I use V8 Free.

Thanks to let me know what's wrong. Answers can be in French or in english, doen't matter.