physical memory is real silicon bits and bytes in a memory chip located in a memory slot on your motherboard.
virtual memory is "pagefile.sys" on your hard drive, pretending to be real memory, aided by your operating system, by swapping portions of your physical memory in and out of the hard drive. This allows your computer to pretend that it has way more that the pitiful amount of actual memory it has.
Not sure if extended memory has much meaning outside of DOS. It used to be that 8086 gen processors could only access a certain amount of memory using the address lines it had. Any additional memory had to be accessed through a memory mapped block whose address could be adjusted to mimic any piece of actual memory.
TTFN