XYZ Summon

Hi guys,
Maybe this can sound a little bit Noob but can someone explain me the XYZ summon?

I didn't see the last yu-gi-ok serie and i don't understand it.

I've several questions
-The mosntrers that after the XYZ summon are still in teh field? (Like if i use change heart and then use the card that i chose to a XYZ summon, at the end of the turn does the card return to his owner?)
-What are the best XYZ cards?
-And other things taht you think that are important to this topic

Thank You

When a monster is used to create a Xyz monster it becomes Xyz Material (no longer a Monster/Spell/Trap Card) and it stays attached to the monster underneath it. Yet it's not considered to be on the field, which means that when you detach to activate a Xyz monster effect you don't get effects like Sangan. These material are like "batteries" or "bullets" of the Xyz Monster, if you use then all, most of them can't use their eff.

THere is no "best Xyz" yet some are better than others. You must see the deck you are using and what options are available to you. You must be sure you can put too monsters of the Same level at same time to consider using a Xyz Monster of the Rank equal to the level of the card.

It's important to notice that Xyz Monsters have no level, instead they have Rank. THat noted they are immune to any effect that involve Levels. For more information you should check this wiki topic; http://yugioh.wikia.com/wiki/Xyz_Monster.

EDIT: On a Side note I also recommend this Article writen by Alikaey, he explains both SYnchros and Xyz in details: http://www.duelacademy.net/t30625-the-black-and-white-universe-synchro-and-xyz

Thank You ))))))