Slot

How can I set a item to a slot?

For example: $inv->addItem(clone $item);

Will add the item, but how can I set the slot?

Try:

PHP:

$inv->setItem($slotId, $someItem);

http://docs.pocketmine.net/d5/dc4/classpocketmine_1_1inventory_1_1_base_inventory.html

Also how can I get the X Y Z of the block a player touches (player interact event)

PHP:

public function interact(PlayerInteractEvent $event){
  $x = $event->getBlock()->getX();
  //and so on..
}

its just the same how you get the coordinates in PlayerMoveEvent.

$event->getPlayer()->x ... y ... z ...

That would get player cords... I wanted to get the "tapped" block xD

this is the correct one: