Blender is only using one tile and only on CPU I have tried to make blender faster by using my Nvidia GeForce GPU in the user preferences window and under the render options in the properties window.
But I can see in the task manager that the CPU is used mostly and even though it is set on multiple tiles it is still using only one. How could I increase the GPU usage and the amount of tiles? Thank you for the answers:)
Switch on GPU compute in the task manager. That will show you something else ;-) GPU compute is different than realtime rendering to task manager. It shows 97% to me while GPU 3D is barely working.

Go to GPU click on one of the sub diagrams like copy and select compute_0 or 1 or whatever yours is called.

be aware that you need something like 1080 before it is faster than a modern day cpu with 4-8 cores.