The IPlayer interface allows you to view certain information on a specific player and interact with said one. Mostly used in Event Handlers and Recipe Functions.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.player.IPlayer;

IPlayer extends IEntityLivingBase. That means all functions available to IEntityLivingBase Objects also are available to IPlayer Objects.
IPlayer also extends IUser. That means all functions available to IUser Objects also are available to IPlayer Objects.

Zengetters are for retrieving information. Usually either assigned to a variable or used in a method/function.

Zengetter	역할	반환 타입	Usage
Zengetter uuid	역할 returns the player's UUID	반환 타입 string	Usage player.uuid
Zengetter name	역할 returns the player's name	반환 타입 string	Usage player.name
Zengetter data	역할 returns the player's data	반환 타입 IData	Usage player.data
Zengetter xp	역할 returns the player's experience level. Can also be used to set a player's experience level	반환 타입 int	Usage player.xp
Zengetter hotbarSize	역할 returns the player's hotbar size	반환 타입 int	Usage player.hotbarSize
Zengetter inventorySize	역할 returns the player's inventory size	반환 타입 int	Usage player.inventorySize
Zengetter currentItem	역할 returns the item the player is currently holding	반환 타입 IItemStack	Usage player.currentItem
Zengetter creative	역할 returns if the player is currently in creative mode (a.k.a gamemode 1)	반환 타입 bool	Usage player.creative
Zengetter adventure	역할 returns if the player is currently in adventure mode (a.k.a gamemode 2)	반환 타입 bool	Usage player.adventure
Zengetter x	역할 returns the player's current X position in the world	반환 타입 double	Usage player.x
Zengetter y	역할 returns the player's current y position in the world	반환 타입 double	Usage player.y
Zengetter z	역할 returns the player's current z position in the world	반환 타입 double	Usage player.z
Zengetter position	역할 returns the player's current position. Can also be used to set a player's position	반환 타입 Position3f	Usage player.position
Zengetter foodStats	역할 returns the player's foodstats.	반환 타입 IFoodStats	Usage player.foodStats
Zengetter bedLocation	역할 returns the location of the player's bed.	반환 타입 IBlockPos	Usage player.bedLocation
Zengetter fishHook	역할 returns the player's fishingrod entity.	반환 타입 [IEntityFishHook ](/Vanilla/Entities/IEntityFishHook /)	Usage player.fishHook
Zengetter foodStats	역할 returns the player's foodstats.	반환 타입 IFoodStats	Usage player.foodStats

ZenMethods are for doing things with other things, in this case with a player.

ZenMethod	Parameter Type(s)	역할	예제
ZenMethod removeXP(XPtoRemove)	Parameter Type(s) int	역할 Removes the given experience levels from the player.	예제 player.removeXP(1)
ZenMethod update(IData)	Parameter Type(s) IData	역할 Updates the playerdata to the provided IData.	예제 ​
ZenMethod sendChat(Message)	Parameter Type(s) string OR IChatMessage	역할 Sends the player a Chat Message.	예제 player.sendChat("Hello my old friend")
ZenMethod sendStatusMessage(message, hotbar)	Parameter Type(s) string OR IFormattedText	역할 Sends the player a status message, if the hotbar argument is true, the message will be displayed on player's hotbar, the default value is true	예제 player.sendStatusMessage("hello, world")
ZenMethod sendRichTextStatusMessage(message, hotbar)	Parameter Type(s) ITextComponent	역할 same as sendStatusMessage, but the message is an ITextComponent	예제 ​
ZenMethod getHotbarStack(index)	Parameter Type(s) int	역할 Returns the item at the given index within the player's hotbar.	예제 player.getHotbarStack(3)
ZenMethod getInventoryStack(index)	Parameter Type(s) int	역할 Returns the item at the given index within the player's inventory.	예제 player.getInventoryStack(3)
ZenMethod give(item)	Parameter Type(s) IItemStack	역할 Give the player the provided item. Item is an IItemStack.	예제 player.give(<minecraft:gold_ingot>)
ZenMethod teleport(position)	Parameter Type(s) Position3f	역할 Teleports the player to the provided position in the same dimension	예제 player.teleport(position)
ZenMethod executeCommand(raw)	Parameter Type(s) string	역할 Executes the command as the player	예제 player.executeCommand("kill")
ZenMethod dropItem(dropAll)	Parameter Type(s) bool	역할 Drops the current item (or the entire stack) that the player is holding.	예제 player.dropItem(false)
ZenMethod dropItem(itemToDrop)	Parameter Type(s) IItemStack	역할 Drops the provided item at the player's position.	예제 player.dropItem(<minecraft:dirt>)
ZenMethod getCooldown(item)	Parameter Type(s) IItemStack	역할 Gets current cooldown of specific item for the player	예제 player.getCooldown(<minecraft:ender_pearl>)
ZenMethod setCooldown(item, time)	Parameter Type(s) IItemStack, int	역할 Sets cooldown time of specific item for the player	예제 player.setCooldown(<minecraft:ender_pearl>, 3)