How do I use load.json and tick.json?

I want my datapack to make a scoreboard for every player and make it visible whenever they join. I have heard some things about load.json and tick.json but don't know how to apply and use them or even if they exist still. I have tried some things and the setup I currently have can be seen in the picture attached, however it doesn't seem to work. How would I use load.json or tick.json correctly or are there even better ways of doing what I'm after?