What exactly is a multifunction tester, and what does it do?

Hey everyone..
I’m about to start messing around with this tool soon, but I’ve honestly never even laid eyes on one before, let alone figured out what it actually does. From what I can gather, it spits out some kind of readout similar to an OBDII scanner used for car diagnostics.. but my line of work involves electrical appliances.
So, what am I actually measuring here?
What's the point of all this?
And how do I actually use it?
Also, why is the sky blue...😁

So, if you check out this pic😠, what you're looking at is basically a bee efficiency tracker—it just counts how many times they fly in and out of the hive!😁😵🙏🤦

Can't really snap a photo right now... looks like some huge old boot, lives totally solo, doesn't move much, and barely eats anything at all..
I’m asking the people who actually know their stuff... you don't even need to see the power running to know exactly what we're dealing with here