Why multithreading can be leveraged to multicore?

I recently review the basic knowledge, just met a friend asked me this question, so by the way to make a record, consolidate under

• The first is to review the difference between the thread and the process.
  • The main point is that the process is the smallest unit of resource allocation, and the thread is the smallest unit of CPU scheduling. (one is equivalent to a container, one is specific to the CPU operation)
  • Inter-process resources are not shared, and multiple threads are sharing resources allocated by the same process.
• Because threads are split between user threads and kernel threads. Kernel threads can go to different cores to operate when they are called again. So multithreading is available to multi-core.

Why multithreading can be leveraged to multicore?