Simple way to explain is.
1) Human body =microcontroller
Human brain = microprocessor
2)Microcontroller=microprocessor + memory+ I/O
3) micro is related with the size as the transistors (MOSFETS) have size in 0.000001 cm.
4) microprocessor is use where CPU need to deals with large data (ex.computer)
5)microcontroller is use where IO work is more and deals with smaller data ( single purpose electronic device, automations)