How to Boot up my build PC

[actssassin]

Hey guys I finally built my pc. Its a ryzen 1600, gtx 770 4gb and a 500 semi modular 80+ bronze psu. So I setup all the power connectors to the motherboard including the gpu, cpu power, case fans, hdd etc.
The hdd is from my old pc system which I bought from best buy. It didn't have any other storage, so I think the OS was installed in the hard-drive.
My pc doesnt have an optical drive.
My question is how do I boot up my pc and install the motherboard? My motherboard is a MSI B350 tomahawk which came with a cd. Do I need to get an optical drive to boot up?
Thanks this is my first time building any help would be appreciated.

 

[CountMike]

If it's booting to BIOS you need an OS to run it. If you think that HDD has OS installed, just set it as first BOOT device in BIOS but most probably will not work if installed on another computer.
In that case you would need an installation of your OS of choice on USB stick.