IMPOSIBLE HACER SESIÓN MULTICÁMARA

Yes, please give the OS, media, and steps you're using, and where it's seeming to go wrong.

Mutlicam can be a right puzzler especially until you understand what each option actually does, compared to what it looks like it would do.

Could you provide more details of what is not working for you?

You may alreday be following the appropriate steps but am providing the Adobe support page in case:
https://helpx.adobe.com/premiere-pro/using/create-multi-camera-source-sequence.html 

You can provide screenshots as well to help explain the particular issue you're facing.