Hopefully you have built one of these simple electromagnets somewhere along your journey to become an educated human being. If you understand the basic principle of how an electromagnet works, then you can understand how wireless inductive charging works. In an electromagnet, the flow of electrons (current) causes a magnetic field. The magnetic field forms at a right angle to the direction of the current (the right hand rule). That means as the current flows in a circle around the nail (the fingers of your right hand wrap around the nail), the magnetic field forms along the nail (your right thumb points in the direction of the magnetic field) putting the poles on either end of the nail. If you’ve built one of these basic nail magnets, then you intuitively understand this already.
Here’s the really cool part. This relationship between current and magnetism works in reverse. A fluctuating magnetic field will also create a current in an otherwise dormant wire. Sustain the situation and you will eventually produce enough current to charge a battery. This is usually done with two coils of wire similar to the ones you wrapped around that nail to make an electromagnet. One of the coils is hooked to a power source and the other coil is hooked to whatever it is you’re trying to charge. The coil connected to the power source becomes an electromagnet that is switched on and off at very high frequency. This transforms the electrical energy into a usable form of magnetic energy. When the second coil is in range of the fluctuating magnetic field of the first coil, it transforms the magnetic energy back into electrical energy like an inverse electromagnet. Rapidly turning the electromagnet on and off allows you to broadcast energy as a magnetic field that can travel through the air without a physical wire connection. Check out this video from Veritasium to see how these principles were first discovered and a rad magically illuminated floating grill that would be perfect in a science nerd man cave.
Source: Veritasium on YouTube via IO9