In Yu-Gi-Oh card game, players can play their monster cards by some ways, and those can be roughly divided into the following two groups:
Summons requiring the right to summon
Summons not requiring the right to summon
Special Summons (Ritual/Fusion/Synchro/Xyz/Pendulum)
Right to Summon
The Right to Summon is the term that is unofficially used only in Japan and that refers to the capability of a player to conduct a normal/tribute summon or a set per turn.
Normal summon is the act that players place a monster card from the hand to the field in face-up attack position without using any card effects.
Players can play one normal monster card or one effect monster card in this way per term (some of effect monster card cannot be played like that since those cards requires a specific process to be summoned).
Players can conduct one normal summon or one set per turn.
Basically, players cannot play a monster card in face-up defense position or face-down attack position.
Set is the act that players use a monster card from their hand to the field in face-down position.
Set is not considered as summon. That means a monster's effect which is activated due to the summon of itself cannot be used (Monster cards cannot use their effects in face-down position usually).
Summoning a monster in face-up attack position without any card effects
Placing a monster in face-down defense position without any card effects
Summoning a monster in face-down attack/face-up defense position without any card effects
Flip summon is the act that players switch a monster's faced-down defense position to face-up attack position.
Changing from face-down defense to face-up defense is not allowed.
Flip summon can be conducted without the right to summon or any card effects.
A monster card that is set to the field in a turn is not subject to flip summon during the same turn.
To conduct a normal summon or a set for a monster card with level 5 or higher, players have to tribute a monster or multiple monsters on your side of the field.