Can all of the GPIO pins on the raspberry pi 3 be used as both analog and digital pins? Are there any dedicated analog or digital pins?
Adding to Steve's answer. While all GPIO pins offer only digital input or output, PWM can be used (with very little external circuitry - a low-pass-filter) to at least output analog signals. The Pi has two dedicated hardware PWM pins and may further use the other GPIO pins for software PWM. Some of the interface libraries, such as pigpio or wiringPi, support this feature. This is also the way the Raspberry Pi outputs analog audio.
Other than that analog input or output will require hardware add-ons such as HATs to do so.