Low level I/O access using outb and inb

Question

i'm having hard time trying to understand how interrupts work.

the code below initialize the Programmable Interrupt Controller

  #define PIC0_CTRL 0x20    /* Master PIC control register address. */
  #define PIC0_DATA 0x21    /* Master PIC data register address. */

  /* Mask all interrupts*/
  outb (PIC0_DATA, 0xff);

  /* Initialize master. */
  outb (PIC0_CTRL, 0x11); /* ICW1: single mode, edge triggered, expect ICW4. */
  outb (PIC0_DATA, 0x20); /* ICW2: line IR0...7 -> irq 0x20...0x27. */
  outb (PIC0_DATA, 0x04); /* ICW3: slave PIC on line IR2. */
  outb (PIC0_DATA, 0x01); /* ICW4: 8086 mode, normal EOI, non-buffered. */

  /* Unmask all interrupts. */
  outb (PIC0_DATA, 0x00);

can someone explain to me how it works:

-the role of outb (i didn't understand the linux man)

-the addresses and their meaning

another unrelated question,i read that outb and inb are for port-mapped I/O, can we use memory-mapped I/o for doing Input/output communication?

thanks.