Look for the 'boot order' section of BIOS, and use the instructions on the screen to change boot order to allow for booting from your external. Depending on your OS, it'll probably be F9 to change boot device upon startup...
Thank you for your answer. In the end what I have done is put windows on a flash drive and installed it onto my new ssd from there, erasing all information on it, but now, when booting from the new ssd which apparently has windows on it, it doesn't work. It just takes me to a blue page saying I need to repair my pc.Look for the 'boot order' section of BIOS, and use the instructions on the screen to change boot order to allow for booting from your external. Depending on your OS, it'll probably be F9 to change boot device upon startup...