Microchip manufacture a series        of microcontrollers called PIC.  You can see the range of their        microcontrollers        here.  There        are many different flavours available, some basic low memory types, going        right up through to ones that have Analogue - To- Digital converters and        even PWM built in.  I am going to concentrate on the 16F84 PIC.         Once you have learnt how to program one type of PIC, learning the rest is        easy.       
There are several ways of programming the PIC - using BASIC, C, or Assembly Language. I am going to show you the Assembly Language. Don't be put off by this. There are only 35 instructions to learn, and it is the cheapest way to program the PICs, as you do not need any extra software other than the freebies.
The 16F84 Pins
Below is a diagram showing the pin-outs of the PIC 16F84. I will go through each pin, explaining what each is used for.