Normal Summon (通常召喚 Tsūjō Shōkan, somtimes simply called Summon in OCG) is the most common way to Summon monsters. It can only be performed when the game state is open during your Main Phase. You simply play a monster directly from your hand onto the Monster Card Zone in face-up Attack Position. Gemini monsters can be Normal Summoned a second time while they are face-up on the field.
If the monster you want to Normal Summon from your hand is Level 5 or higher, you must Tribute another monster(s) you control first and then “Tribute Summon” the monster. Level 5 and 6 require one Tribute, while Level 7 and higher require two Tributes.
You cannot Normal Summon Special Summon Monsters.
Some cards can change the Normal Summoning rules. For example, "Ultimate Offering" allows you Normal Summon extra monster, and it lets you Normal Summon during your opponent's Battle Phase. "Light of Intervention" will allow you to Normal Summon in Defense Position.