If you're wondering whether to turn on your mixer or your speakers first, the answer is: it depends. If you're using active (powered) speakers, then you'll need to power them on first, before turning on your mixer. On the other hand, if you're using passive (unpowered) speakers, then you'll need to turn on your mixer first, before powering on the speakers.
The reason for this is that powered speakers have their own amplifiers built in, so they need to be turned on first in order to work. Passive speakers don't have their own amplifiers, so they rely on the amplifier in your mixer to function. That's why you need to make sure that your mixer is turned on before powering up passive speakers.