2.) Select the dinosaur in the pen you wish to tame. There will be a small 'Items' Icon' button located on the right side of the screen. Click this.
3.) A new screen will appear that looks like a 'Dress Up' screen. Drag and drop a Lead Item to an OPEN SLOT on the left.
4.) Click the red button that states 'USE ITEMS'.
5.) You will be taken to a list of all the animals in that pen. Pick the one that has the Lead or Collar (it should say 'Wearing Lead/Collar) and hit 'USE'
6.) It will take several in game hours to tame the dino, based on the creatures temperament. While taming, you must have food that the dinosaur likes in it's nearby food trough and the dinosaur must be kept happy.