Acronym v abbreviation

An acronym is when an abbreviation forms a pronounceable "word". Nato stands for the North Atlantic Treaty Organisation, and is pronounced as if it were a word. FAQ, Unicef, Unesco, radar, Euratom  and LOL are also acronyms. One of them (radar) is now treated as an ordinary word. 

An abbreviation is not pronounced as a word. Instead, you must pronounce each letter separately:  BBC, UN, EU, LBGQT+, JCU,  etc.

An acronym (pronounced as a word) is treated as a proper noun (like a name) and therefore does not take the definite article.

An abbreviation, for which you must spell out the letters, is not treated as a proper noun, and therefore can take the definite article.

Accordingly, we say NATO is... but the BBC is the propaganda arm of the British government, the UN is an international body etc..

If you are a Romance-language speaker, you need to be careful of this, because Romance languages often pronounce turn abbreviations (which  take the definite article) into acronyms (which do not). 

Finally, to dot or not to dot?  

Back in the day, we were supposed to write B.B.C. with all the dots instead of BBC; likewise, it used to be  U.S.A., U.N. and so on. Mercifully, the dots have pretty much disappeared.