Hello I'm going to guess from your username that your birthyear is 2001, making you a cadet? If so, when you join a cadet unit, you'll be measured for a uniform. Depending on the unit and your sizing, it may need to be ordered, or they may kit you out from stock on hand. You'll likely have a uniform fairly quickly. The unit supply officer will make sure you have everything you need, and other, more senior cadets, will teach you how to wear and maintain it correctly.
I can't answer your questions about your parade location, but I'll guess you will have some sort of orientation to what may become your home away from home for years to come.