I just finished my first build and I turned the PC to check how everything works, it turns on but there is a Solid Orange light at the bottom of the motherboard, It has 2 lights one at the top which turns white and the other one. I can´t check if it POST since my GPU arrives tomorrow.
There is no OS yet.
I´add a pic a bit, my phone is charging rn.
Motherboard: Asus ROG Strix B350-F
That's probably your standby LED. It's pretty standard on ASUS boards. My sibling's ASUS Z77 board has that on when the system has power. Nothing to worry about.