Pins with Multiple Functions

Using Arduino Microcontrollers
#1

I am using an ESP32 Pico Kit V4.

If the pins are all being used for several functions, how do I know that I'm not stepping on the toes of a pin by using it as input or output? Do I need to know and understand all of the pins functions before choosing pins?

Is this why we use pinMode()?

I do know if you try to use the serial pins it certainly will have problems doing two things at once. How about the other pins?

#2

If you are using the pin for one of the special functions, it can't be used for general I/O. This is the same as a normal Arduino (ex, on the uno if you're using A4/A5 for I2C, you can't use them for general I/O).

The pins that are connected to something important that you can never use as general I/O are noted with a footnote on that table.

#3