It depends on your map format. Similarly to how you know how to read in model data, you need to know how to read in the format of your map. You need to know how the file is organized and where everything is located. For example, I use a custom format in my engine where the header contains the map's background music and tileset. If someone wants to write a reader for my map, they need to know what that header looks like.
You have the concept right. You basically have two classes, your node class and your linkedList class. The node class contains your data as well as a pointer to a node object, which is the next node in the list. The linked list class has 3 node pointers, a firstNode, a lastNode and a currentNode. The firstNode is the first node in the list, or the head. lastNode is the last node in the list, or the tail. currentNode is used to iterate through the list by grabbing the memory addresses of each subsequent node.
The reason you only need three nodes and not one for each piece of data is because each node exists within its previous node. So if you have 5 nodes, you have your head, which contains a pointer to the second node, which contains a pointer to the 3rd, which contains a pointer to the 4th, which contains a pointer to the 5th (the tail).
I threw a breakpoint in where I'm actually checking the state of the key. It doesn't break when I press a letter key, but it does for others. I'll look into GetKeyboardState()
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