Hi and welcome to the forum.

In my experience, the way you do reference letters varies by country. In the US, you normally ask a teacher or former boss (or co-worker sometimes) if you can use their name as a reference. Then, when you apply for a job and they ask for references, you give that person's name and contact information (address, phone number, e-mail) so that the potential employer can contact them to ask about you.

In Germany, you get a letter from your boss or teacher that you take with you to interviews. It's done as a "to whom it may concern" letter - but the disadvantage is that because the person gives the letter to you, they generally can't be real open about both your strengths and weaknesses.

As someone doing the hiring, I never liked getting those "to whom it may concern" letters because generally the person wrote the letter themselves and just asked the person giving the reference to sign it. It tends to mean much more if a job candidate can give you a contact number for their reference so you can call and discuss the candidate.

Just as an aside, when job hunting in the US, I always notified my references when I had given out their name and gave them some information about the job I was up for. A good reference can tailor what they say when contacted to the job you're being considered for.
Cheers,
Bev