Hello there!
Well, in order to learn about the MCU and assembly, my suggestion is to buy a kit of one MCU of your selection (maybe PIC, AVR or any other) and start playing with it! Most of the software programs for programming in assembly (like the MPLAB for PIC) come with various examples that you can study in order to learn the different capabilities of the MCU and the assembly language.
Perhaps, the simplest project to start with, would be to connect some LEDs to the MCU and play with them. Again, this is an example that most assemblers are shipped with.
I hope I have helped you!