Have you read the documentation? Take a read of this: https://nodered.org/docs/user-guide/contexttake and then if you don't understand ask.
You can also read this post I made quite awhile ago: (A guide to understanding 'Persistent Context')
Have you read the documentation? Take a read of this: https://nodered.org/docs/user-guide/contexttake and then if you don't understand ask.
You can also read this post I made quite awhile ago: (A guide to understanding 'Persistent Context')