i dont undertsand ultimate offering effect i think either player can do an extra summon?

Answer 1

No. You may be looking at an older version of it. The new text says: By paying 500 Life Points, Normal Summon or Set 1 extra monster. You can only activate this effect during your Main Phase or your opponent's Battle Phase. When a card says "you" it means the controller of the card.

Go to http://www.netrep.net for card rulings and info. Alot of cards got new text when Dark Beginnings and Dark Revelations were released and the new text is on NetRep.

Answer 2

Ultimate Offering - for those who don't know, this is a Continuous Trap Card in the Yu-Gi-Oh! Trading Card Game - is activated when you flip it face up, better when your opponent's turn ends. Ultimate offering allows an extra Normal Summoning (Tribute Summon is considered as a Normal Summon) or Set after your first true Normal Summon that costs 500 of your Life Points each. For example: I played E-Hero Wildheard as a Normal Summon, next using the effects of Ultimate Offering, by paying 500 of my Life Points, I summon Mobius the Frost Monarch by Tributing my face-up Magician of Faith, then I pay another 500 to set (Face down in Defense Position) Mask of Darkness. Check out NetRep for more info.