The letters are pronounced separately, as in BBC (/biːbiːˈsiː/), CBS /siːbiːˈes/, etc. The idea is obviously to abbreviate, i.e. save time, but the Internet's WWW (double-u double-u double-u, pronounced /ˈdʌbəl.juː ˈdʌbəl.juː ˈdʌbəl.juː/) actually takes longer to say than its component words.
Students - and teachers - need to be well aware that initials and abbreviations, like words, can change over time and that, as usual, context is fundamental. In Britain, PC for many years stood for "police constable", before becoming "personal computer" and nowadays also standing for "politically correct". Likewise ATM, which still stands for "automated teller machine" has recently also come to stand for "air traffic management". And the relatively recent IT has now become ICT.
If asked to "initial" a document, particularly to approve or endorse it, you should write the first letters of your name, e.g. "Jonathan Miller" would write "JM".
|BBC||(British Broadcasting Corporation)|
|EFL||(English as a Foreign Language)|
- Usage in American English and British English tends to differ. In the former, many people use the term acronym as a synonym for initials, whereas British English considers an acronym an actual word corresponding to syllables, as in radar, NATO, etc.