I recently began using 3D tracking AF on my D3300 and it can be interesting. In a good way.
I got my DSLR to photograph Grand Kids, and Humming Birds.
Both (as you know) move a LOT.
Watch this
Youtube tutorial.Or, closer to your particular model:
D5200/5300 Focusing modes.But, note that Michael talks about being in the P,S,A,M modes.
If you are in any of the other modes, the camera takes away your choices, and uses it's choices.
And that can get terribly confusing. It sure was for me. And the camera usually picked the wrong spot.
So watch, rewind, watch with camera in hand, pause while you find and set the camera.
In AF-C (continuous) Mode, with 3D tracking is what I'm using for soccer games and my birds now. So far, sooo good.
And in "P" (programed) Mode.
Gene posted a link to a most outstanding article about focusing modes explained.
http://photographylife.com/dslr-autofocus-modes-explainedI read through it, then picked up my camera and began applying it. When I had the camera set I went out and Bam!
Got the shot I wanted.
http://www.uglyhedgehog.com/t-279550-1.htmlGood luck and don't be shy about asking questions. Your questions help me, and others learn as well. ;)