Something precise is neat and tidy, or very detailed, or perfectly exact.
A precise rule or a set of precise instructions tells you exactly what to do. A precise plan lists exactly what you're going to do, and when, and how. And a precise scale, like the one pictured below, tells you exactly how much something weighs. This fruit salad weighs precisely 162 grams.
How many jelly beans do you think are in this jar? If you said, "Eh, about a thousand," then you gave an estimate. And if you counted them and said, "This jar contains precisely 1,217 jelly beans," then you gave a precise answer.
It's good to be precise—to use precision—when you talk and when you write. When you give precise details and precise information, then people know exactly what you mean. If I say, "My cat is fluffy and nice," then that's not very precise, so you don't know much about her. But if I say, "My cat Layla is covered in white and gray fluff, and she loves to sit next to me and purr," then I'm being more precise, giving you detailed information. Now you know a lot about Layla!
(Source: personal photo)
The opposite of precision is vagueness or generality. Let's say I'm going to the grocery store, and you ask me, "Hey, can you grab some snacks for me? Something yummy." Well, that's not very precise: that's vague, or general. I don't know what to get you!
But if you're precise, you'll say something like, "Can you grab me some ripe bananas and a jar of salted peanuts?" That's a precise request! Which is great, because now I know precisely what to get. And we're both happy!