Two free GPS apps that give verbal turn-by-turn navigation are amAze and Nav4all. Google the names to find links. I don't use either and can't tell you which you might prefer. There are not many free choices with verbal turn-by-turn.
Don't forget Life in Pocket as well. Their newest version is pretty good, some quirks. Amaze is free only for the older version 4.2 (I think). The older version is also very hard to navigate. So much so, that lots of people have simply given up on it (i Like it). The newer 5.0 version is not free.