Biometric Enrolment letter

Hello everyone
my name is Federico, i went to the post office for do my Bio metric information but the officer ask me to show him my Bio metric Enrollment letter, from that moment my frustration went at very high level. He told me to go on line and apply for this Bio metric Enrollment letter but after few days of stress, i didn't find no one useful information. could someone please help me about the application for Bio metric Enrollment letter.
i found a lot of information about the process works but not one information about how apply for.
kind regards
Federico

What application have you made to the Home Office?

When did you make the application??

You don't apply for a biometric enrollment.
The Home Office will send you a special letter *after* you have made an immigration application, for example, for a permanent residence card. That letter has a barcode that the post office employee would have to scan to be able to take your biometric data.
If you have never made an immigration application to the Home Office, you don't need to have biometric enrollment. If you have, then wait for the letter from them.
That said, European Union citizens are often/usually exempt from it anyway.