The sync type defines the method of syncing, you have the option of selecting one of layers movie time, object rotation, and movie time plus rotation.
Sync to defines which fixture you are syncing to. Each fixture will need to have a unique fixture ID set.
For example, if you have 3 DL3 fixtures, all of them playing back a movie file on layer one, you can set fixtures 2 and 3 to have a sync type of layer one, with a sync to of fixture ID 1. This will sync the playback of those two fixtures to the fist one.
In order for syncing to work properly, be sure you are running the latest software. It is also imperative that your custom content be encoded in accordance to our specifications. Specifically that they be encoded as elementary streams with all I-frames.