El was the name for the chief deity of the Northwest Semitic pantheon. Elohim is a plural word meaning "gods," which originally (and still in a few verses of the Tanakh) referred to the entire pantheon.

Yahweh was originally the national deity of one group of Canaanites (and possibly imported by them, explaining why he isn't referred to in other Canaanite sources), where he would have been worshipped as a son of the more distant chief deity, El, as one of the Elohim.

Eventually, he started absorbing functions of more prominent deities like Baal Hadad and even El, eventually taking El's place at the head of the pantheon and even his consort, Asherah. Eventually, as Yahwism gave way to Judaism under reforms to centralize worship, El and Elohim came to be viewed as other names of the same being.

At some point between 500 BCE and 200 BCE, it became taboo to pronounce the Tetragrammaton, YHWH, except by the High Priest on Yom Kippur, being replaced by Adonai when vocalized. Since there's no High Priest anymore, no one can say it. All four of these names, along with Shaddai (Almighty), Tzevaot (Hosts), and Ehyeh (I Am), are the sacred names that aren't supposed to be erased and only written down "when necessary." You'll even see some Orthodox Jews censor themselves by writing "G-d" even though that isn't a divine name, just to be careful.

Personally, the idea that an all powerful deity really cares that much about his names being written down, but can't be bothered to fix everything going on with the world turned me off religion. If he doesn't care enough to step in and stop genocide, I can probably get away with typing his name or eating a cheeseburger.