The Programmer is the temporary place for your values. This is where the values are kept until you store them somewhere or throw them away.
The Programmer have several levels. When you select a fixture the fixture ID number turns yellow in the fixture view. You can change the values of the selected fixtures by moving the level wheel or any other way you can change the values. When you have active values in your programmer they get a red background in the Fixture view (sheet mode). You'll also see red markers in the Preset Type Bar.
When you store something you still have the values in your programmer - they are just not considered active anymore.
When you have a selection and values in your programmer, then you can press the Clear key once to remove the selection and Clear once more to release the values from the programmer.
If you just want to release something specific you can use the Off key and then press what you want to release - to learn more about off please read about the Off key.
The Programmer have a higher priority that the executors. This means that if you have a values in your programmer, then it will not be overwritten by the cues.
You can hide the values in the programmer from the output by pressing the Blind key. And bring it back to the output also by pressing Blind.