Thanks for the reply.
I have two yongnuo 560 iii flashes and can't get them to trigger without putting a trigger onto the shoe which then blocks the cameras flash.
I'm after the cameras built in flash to work and a flash lite to be triggered from behind the object fine with this being a manual flash.
I'm still not sure if this is possible with the d3300, am I right in thinking it needs command. The type of thing I'm after is in this video with the guy using a nikon d330 is that more like the camera I need?
https://m.youtube.com/watch?v=AVBhnJnDcnM
It is easily possible, but your video link is using a camera with Commander. The d3xxx models do not have a commander (and most 560 models do not work with Commander anyway ... I think the EX might?). So you have to use Manual flash instead.
In that menu where the video selected Commander, instead you have to select Manual flash mode. Then you set the camera flash level there too. It can be quite low level just to trigger the remote, but if you want the internal flash to also contribute light into your picture, then you have to worry with the proper level.
Set the 560 remote flash to its S1 trigger mode, and it will trigger in sync (from the Manual camera flash).
If you leave the internal flash in TTL mode, you have to use 560 S2 mode instead (and the internal flash will try to fully contribute). The 560 is still manual flash of course. It is essential to understand the difference in TTL and Manual flash.
An alternative would be to replace the camera flash with a hot shoe flash that provides a commander function, like the SB-700 can be a commander (or the Nikon SU-800 is a commander). However, the D3xxx camera models still do not have the FV Lock function, which is rather essential for human portraits, to prevent pictures of their blinking.