Yugioh (1st series), 2nd series (GX- Fusion), 3rd series (5d - Synchro).
Using monster **you control** to special summon a monster from extra deck.
Long story short, (adding) sum up all monster Level. eg: 2* + 3* +3* = lvl 8*.
Watch youtube for easier understanding.
Using tuner monster and Non tunner monster (normal/effect monster) to special summon synchro summon from extra deck. But the level must be correct.btw, synchro summon not cancer. Execpt black wing archtype.hahah
Bad. using 3 cards put into def position.
But as you see comment at below about synchro summon, if duel link expanding it into 3rd series, there is a spell card call "instant fusion" to special summon this card from extra deck, then use it as material.