This guide is for those who want to skip the BS and get straight into laying your conveyor belts underground.
Step 1: Figure out where your conveyor belts are going to go. You will have an input line coming from ticketing desks. Each desk requires its own connection to the conveyor line.
Step 2: You're going to now start with your underground construction. Be sure you have planned out where your conveyor belts are going to run, and yes it is going to be very expensive. Also, you can't run two belts side by side, the gods of time and space just wont let you. Just ignore those teleporting workers.
Step 3: The Baggage Hub. This beast sorts whats coming and going from each baggage depot. There are 6 slots on this thing. The top and bottom connect to other baggage hubs with 2 way conveyor belts. The two input/outputs set which lines the bags are going to come in and go out. You have to click the hub and set between consumer (bags going in) and Producer (bags going out)
Step 4: The Baggage Depot: this thing has to be on the side of a taxiway for the baggage carts from your hangars to get to. This beast is deceptive. This is where a bags journey through your airport begins or ends. These underground connectors will need a line to your consumer port on the hub and a different line going from your producer back to the depot.
Each depot will require its own baggage hub and appropriate connections to each. You will have to assign these to gates.
Underground view, the conveyor belts will start above the input/output of the baggage depot above ground.
Step 5: Hangers. planes don't go in these, your trucks do. there are three sizes, small medium and large. Click on the hanger and buy the vehicle you need.
Step 6: The Up Conveyor transition. This allows your bags to go up to the next floor and onward to the baggage carousel where passengers can pick them up.
There can only be one baggage carousel per conveyor belt, have fun splitting these up when it starts to get crowded.
Summary: Plan to have a lot of money to get this going.
Remember to click the baggage hub and set your input and output. Have a dedicated line for baggage going to pick up and have a line going to ticketing to the hub so the bags get to the planes.
You have to have a square between your lines, they wont let you put them next to each other. Your underground is going to be a long and convoluted series of tunnels getting to the gates and baggage claim.