Working on my second project and I'm confused about proper procedure for turning on the arduino
If you've rewired an Arduino board for a new project, such that outputs from the currently-loaded sketch may cause problems, temporarily jumper from ground to Reset, to hold the MCU (ATmega328, etc.) in reset until you are ready to load the new sketch.  Pull the jumper upon starting a download, of either your new project or an empty sketch as suggested in Majenko's comment.  Typically, Arduinos are reset at the beginning of each download. 

Arduino boards (Uno, Nano, Mega, et al) that use an additional chip (FT232, Atmega16U2 or 32U4, CH340G, etc) as a USB interface should be able to register as USB devices even when the MCU is reset.  Arduino boards without a separate USB chip (Leonardo, Micro, et al) should not.