Prompt tuning and telling is having a moment at the minute. Among the people who use AI as an assistant, at least. But it is worth stopping to say what it actually is. It is not simply a technique for getting work done, and to see the point of it you have to start with why anyone needed it in the first place.
Why it is needed at all
AI behaves differently depending on the company that built it. And you cannot instruct that company to come and fit around the way you work. So the next best thing: at least when the answer comes back to us, let us decide how it comes back. That is prompt tuning. Explaining it in plain words so the AI knows what you want is prompt telling.
I started the same small way
I like the newest thing at the top and the older thing further down. So whatever answer I get, I set it up so the most recent data sits at the top and the oldest sits at the bottom. It started with something that small, and then it was the order of the companies, the order between teams, sales before accounting, all of it fixed the way I want it. Prompt tuning and telling sounds like a large discipline. At the start, mine was only this.

Settings run out
It looks easier to go into the program settings and change these one at a time. But do it for a while and there is too much to fix, and the setting up becomes a job of its own. What it should remember about me. The order I want things done in. The direction I am heading. You cannot put all of that into a settings menu.
So I moved it into memory
Instead of handing over instructions, or saying answer it this way, I now store the things the AI is better off knowing before I give it any work at all. I tell it the formula that produces the answer I want, and on top of that I add what it should remember about my company and about my environment. Then when it works with me, it starts already knowing me accurately. That, to me, is what prompt tuning and telling really is.
Not fixing the answer, but making it remember me.
Prompt telling is the part where you put that memory in, in your own words.
If it still feels vague, ask this
If prompt tuning and telling is still an abstract thing to you, one line to the AI is enough. "I want to fix what you remember about me. How do I do that." Prompt telling starts there.
What memory would you want to fix in your AI?