First, you will need a yo-yo. Any kind will do fine.
If the string is too big, you'll have to tie it.
In this video demonstration, you will see that you pull the string through the loop of the hole and pull it around your finger. This will let you make the string tighter or looser.
There are 2 ways to throw a yo-yo. This is the easier way. All you do is drop the yo-yo down. As it reaches the bottom, use you wrist and flick it up with little force, and catch the yo-yo.
The 2nd way is to let the string go down on your pointer finger as you turn your wrist. When it reaches the bottom, flick your wrist up slightly (with your finger still on the string) and catch it.
This is what your hand should look like as you let it down (and the same for when you bring it up)
If this happened to you, then here is how you wind your yo-yo up for use again:
A demonstration on how to wind your yo-yo up.
And that's the basics of using a yo-yo! Feel free to ask me any questions. Thanks for viewing, hope it helped!