This expression in English shows that there is a contrast between the people Jonah had just spoken about and himself. They paid attention to useless gods but he would worship Yahweh. It can also be translated as "But I."
## I will sacrifice to you with a voice of thanksgiving ##
This means that Jonah would thank God while he offered a sacrifice to him. It is not clear whether Jonah planned to thank God by singing or shouting joyfully.
## Salvation comes from Yahweh ##
"Salvation" is a noun. Its meaning can also be expressed with a verb: Yahweh is the one who saves people."