Pins with Multiple Functions

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?

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.