When I first started looking into microcontrollers (an MCU) it was like trying to sneak into an exclusive club where everyone speaks a secret language. I was excited to learn of all of the great stuff people were doing with Arduino, but a little discouraged at the price. If you'll only ever need one for experiments, then the price is fantastic. If you plan on building them into a lot of different projects it could get pricey. Soon I deduced that the chips that are on the Arduinos can work as a standalone device and can have a much smaller form factor and price. These days there are books and tutorials everywhere explaining how to roll your own Arduino clone. Arduino is awesome, read up on it!
The super basic undetailed outline:
Write some code: gotta do that part in C.
The Arduino IDE (programming software) makes this all so much easier. You could make a text document, compile it into hexadecimal format, and then upload it to your MCU directly through AVRDude, OR just type it up in the IDE and hit the upload button. The other cool thing the IDE does is plug libraries of code into the code you've written just by typing #include <Library name>. There are certain things you might want the MCU to do that would require monstrous amounts of code. If there is a library for it though, you might only have to write one line (vs. 50 lines).
There are some pins on the MCU that you connect to a programmer that's plugged into your computer. The program on your computer turns the code into a bunch of 1's and 0's and sends it down the cable into the MCU to make it do your bidding. Mwa ha ha ha! The Arduinos have some code on them already (a bootloader) that allows them to be programmed through just two pins, RX and TX. Other programmers need to be connected to six pins, but they don't need the bootloader.
Once you have done all that and failed several times, eventually you will be successful, and you will have a little electronic brain to do your bidding. Make stuff automatic. Make stuff smarter. Make stuff be amazing. Make stuff sparkle and blink. Build your own minion.
A quick list of the things you might want the MCU to do:
Turn stuff on/off
Drive DC motors, steppermotors, or servos
Connect to WIFI
Monitor sensors like:
Hmm, lemme think about it a minute, there's more
So the moral of the story is that micro controllers do amazing things and the interwebs are now full info to help n00bs get started. Check the links box over there --->
for resources that I have used to git goin'.
If you end up using and loving the Arduino IDE and think they're an awesome company, buy some kind of Arduino product to support the development of more awesomeness.