A part of a series on English grammar...
Acronyms are formed from the initial letters of several words like some abbreviations are. But unlike abbreviations, acronyms are pronounced as words rather than as just a series of letters.
For example, OPEC (Organisation of Petroleum Producing Countries) is pronounced o-pek and is thus an acronym, unlike USA (United States of America) which is pronounced as a series of letters and not as a word (oo-sa or yoo-sa) and is thus an abbreviation.
Acronyms are written without full stops, as in UNESCO (United Nations Educational, Scientific and Cultural Organisation). Mostly acronyms are written in capital letters, as in NASA.