--WEEKLY :  IC'S YOU NEED TO KNOW---

You'll see this chip a LOT in CV sequencers and bent devices.
Here's why:
It makes things like other IC's and Microcontrollers (Arduino, Rasberry Pi) able to perform the same tasks that analog physical switches can.
For example, you want your Arduino to switch on a light switch.  How can you do it? All the arduino can do is send out 0's and 1's (digital) or PWM/square wave/analog electrical signal/audio/etc..it cannot switch things.
2 options: if its just a simple thing like one light switch you might use a 2n3904 or other simple pnp/npn transistor..or you can use a 4066-and switch on/off multiple things.  In this example, you'd take the 2 leads that are attached to the light switch and connect them to either pin 1&2, 3&4, 10&11, or 8&9--those are the ends of the circuit you want to join or separate.  Then you'd connect either pin 13, 12, 5, or 6 to the Arduino/Raspberry PI/PIC which can then connect or separate the circuit by opening and closing the connection according to whether its sending an UP or DOWN signal to the (13, etc) pin on the 4066.

This, obviously, becomes incredibly useful for sequencers and circuit bends or instrument mods.

Hopefully this simple explanation of the CD4066 can help you understand the chip and gives you some ideas how to employ it fucking up things.

Link to PDF datasheet: HERE IS THE DATASHEET FROM TEXAS INSTRUMENTS FOR THE CD4066