The exclamation means that it is an interrupt capable pin. This simply means that the hardware can directly fire an event w/o the system having to poll for its value. So, if you want some code to run when a button is pushed, then this is the best pin to wire the button to.
@ bioengproject - If asking a very basic question about pull up resistors, such as “what is a pull up resistor”, then reading the document about digital inputs might help.