Whether you need to check in again depends entirely on how your tickets were booked. If your entire journey is under a single booking reference (PNR), you are typically checked in for all segments at your initial departure point. You will receive all your boarding passes at once, and your luggage will be tagged through to your final destination. However, if you "self-transfer" by booking two separate tickets on different airlines, you must exit the secure area, collect your bags, and check in again at the departures desk as if you were starting a brand new trip. International-to-domestic connections in countries like the US also require you to clear customs and re-check bags, though you usually don't need a new boarding pass. Always confirm with the agent at your first check-in counter to see if your bags are "checked through."