Where the alphabet comes from
Mesrop Mashtots created the Armenian alphabet in 405 AD. It had 36 letters; Օ and Ֆ were added in the Middle Ages, and Eastern Armenian spelling counts the ligature և as a letter too — hence 39. The order and the names of the letters have barely changed in sixteen centuries.
Sounds English does not have
Armenian has three series of stops: voiced (Բ, Գ, Դ), plain (Պ, Կ, Տ) and aspirated (Փ, Ք, Թ), said with a puff of air. Ծ/Ց and Ճ/Չ pair up the same way. Ղ is a throaty sound like the French r, Խ is the ch of Scottish loch, Ռ is a rolled r and Ր a single tap.
Eastern and Western Armenian
The letters are the same, but Western Armenian swaps voiced and plain sounds: բարև is “barev” in Yerevan and “parev” in Beirut or Istanbul. The LearnArmenia dictionary gives both pronunciations for every word.
What learners mix up
Ո is “vo” at the start of a word (ոչ — voch) and “o” inside it; Օ is always “o”. The pair ու spells the sound “u”. Ե is “ye” at the start of a word and “e” inside it, and Ը is a short, neutral vowel like the a in “about”.