Yhas a split personality. It can be a vowel (in happy or try, where it stands for the short and long i sounds) or it can be a consonant (as in year). Like a vowel, it works alongside others to create a repertoire of sounds, ay (day, quay, kayak), ey (key, grey), oy (boy, foyer) and uy (buy). But in alphabet friezes, it features in its consonantal form, usually in rather odd borrowings - y for yacht (Dutch), yak (Tibetan) or yoghurt (Turkish). Little wonder it causes problems for children. Y's alphabet name also sounds like why (starting with a w sound); it's at the beginning of the word you, which sounds like the letter u; and the initial y sound in many words is actually made by u (unit, usual). Some children mix up y, w and u for years. Once you're over this soundsymbol hump, there's all that changing y to i when adding an ending (happy-happily, cry-cries). The secret is to remember it doesn't work if y is preceded by a vowel (monkeythe ending begins with i (carrying).
On a lighter note, y sometimes turns up to signify Olde Englishness. It's the nearest shape printers have to the Old English Letter thor, which stood for a th sound. Hence the Ye which precedes olde wishing wells and all things merrie.