When you first go to the configurator, you will be prompted to choose your keyboard. After choosing, you will see a top-down view of the keyboard and a layer selector on the right side.
By clicking on a key, you can customize its behavior by selecting another key or function in the panel that appears below the keyboard. The currently available behaviors are:
- Keys - Individual keys such as letters, numbers, media keys, and function keys.
- Layer - Activate and deactivate layers.
- Modifier - Send multiple modifiers with a single key press or allow a key to be a modifier when held and another key when tapped.
- Special - Behaviors specific to the keyboard.
After you have configured the behaviors to your liking, click the "Compile & Download" button in the top right to download the compiled firmware for your configuration. This typically takes around 30 seconds. You will need to load this compiled firmware onto your keyboard. See step (3) above for instructions.
If you are logged in to Massdrop, you will see a "Save as a New Copy" button next to the "Compile & Download" button. Clicking this button will save your configuration, allowing you to revisit it and modify it. The next time you go to the configurator, you will see your saved configurations above the list of keyboards.
Layers allow you to configure your keyboard with more behaviors than its number of physical keys. For example with the CTRL Keyboard, by default, when you hold Fn + A to change the LED pattern, the keyboard is actually activating Layer 1 and sending the code for switching to the previous LED pattern. The physical key that is mapped to the letter A on Layer 0 is mapped to changing LED patterns on Layer 1.
For each key, its behavior is determined by the highest active layer. For the highest active layer, if the key's behavior is "transparent" (denoted by a grayed-out "(trns)" on the keyboard display), then it falls back to the next-highest layer where its behavior is not transparent.
The QMK documentation has some tips for working with layers: https://docs.qmk.fm/#/feature_advanced_keycodes?id=working-with-layers