Should We Vocalize During Salah and Duas?

As-salamu alaykum everyone! Hope you're all doing well insha'Allah. I've been wondering about something and thought I'd ask-is it necessary to actually make a sound, like a whisper or low voice, when reciting surahs and everything else during salah, or is it okay to just say it in my mind while doing the physical movements? Also, for duas and istighfar, like when I'm just going about my day, can I make these prayers in my head while walking or should I be moving my lips or whispering them out? JazakAllah khair for any help!