First thing is you don't POWER anything with your Arduino. Well, almost anything. LEDs are ok with current limiting resistors. And devices with similar small current requirements may be posered from the 5 volt pin.
But, if you have 24 volt devices. We are assuming that is 24 volt DC! then you need a 24 volt power supply that can supply at least the current needed for your devices.
The Arduino can control a device that uses 24 volts, or can control something like a relay or MOSFET that can control the 24 volts.
Hope that gets you started.
Paul