When it is used as "still" or "yet", you can choose whichever you want.
Example with "still": "Jeg har enda/ennå ikke spist" = "I have still not eaten"
Example with "yet": " De har ikke kommet endå/ennå" = " They have not arrived yet"
However, when used as "even" or "even though", you must use "enda"
Example: " Jeg ble enda sintere" = "I became angrier still" or literal translation: " I became even angrier"
So in summary, just use "enda" and you're good ;) hope that helps