I can't select a single bone in object mode I have been trying to attach the hat to the head bone for almost over 3 hours now and i just can't get it to work.

When i look up tutorials on youtube their bones are grey and available to click on a single bone in object mode, when i click on a bone it selects every bone and the bones are as in the picture (They are not selected in the picture). I think that has something with my problem but i have no idea how to solve it.
I think you are looking for the PoseMode.

The ObjectMode selects always the complete Armature.
In the PoseMode you can rotate, manipulate and add contraints to the bones.