Thank you so much for the useful and quick answer.
After reading your reply I have some doubts yet. Do I have to create a new account at Worpress.com or not? Sorry, but I am not very kind on these matters and I am a bit confused ??
So the steps have to be the following:
1) I have my news domain (I Want just https://www.sergiobarbeira.com, with no wordpress.com in the URL) and hosting.
2) I have to create a new account on WordPress.com??
Thank you!!