That arrow next to what you typed is the next button. Also pressing enter also advances you to next question.
Pressing see answer is just for you if you want to know what it should’ve been. Doesn’t affect the reviews at all. When you get it wrong pressing enter will continue into the next question, and the question you got wrong will come back again at the end of the current queue
And yes, undo is just for typos and the like. If you undo a wrong answer and then enter the correct answer, it will mark it as if you knew it moving it up in srs. Something you don’t want for a question you got wrong