I read how to begin to translate here, but like in this video: https://amara.org/videos/rquDIuCOm8cD/info/introduction-to-electricity/
Do I have to hear and insert the subtitles in English to translate to Portuguese?
Thank you for your question, Fabiano.
It's really up to you: if you wish, you can directly create Portuguese subtitles from the audio. I find it simpler to first create original subtitles, because afterwards, you just have to translate them. And if you make English subtitles, they will be a help for other translators too.
In this case, though, there are already automatic English subtitles on the original YouTube video. So I downloaded them for you (see attachment). You can now upload them to the Amara video, and correct possible errors.