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	What does it do	戻り値	Usage
Zengetter uuid	What does it do は、プレイヤーの UUID を返します。	戻り値 string	Usage player.uuid
Zengetter name	What does it do returns the player's name	戻り値 string	Usage player.name
Zengetter data	What does it do returns the player's data	戻り値 IData	Usage player.data
Zengetter xp	What does it do returns the player's experience level. Can also be used to set a player's experience level	戻り値 int	Usage player.xp
Zengetter hotbarSize	What does it do returns the player's hotbar size	戻り値 int	Usage player.hotbarSize
Zengetter inventorySize	What does it do returns the player's inventory size	戻り値 int	Usage player.inventorySize
Zengetter currentItem	What does it do returns the item the player is currently holding	戻り値 IItemStack	Usage player.currentItem
Zengetter creative	What does it do returns if the player is currently in creative mode (a.k.a gamemode 1)	戻り値 bool	Usage player.creative
Zengetter adventure	What does it do returns if the player is currently in adventure mode (a.k.a gamemode 2)	戻り値 bool	Usage player.adventure
Zengetter x	What does it do returns the player's current X position in the world	戻り値 double	Usage player.x
Zengetter y	What does it do returns the player's current y position in the world	戻り値 double	Usage player.y
Zengetter z	What does it do returns the player's current z position in the world	戻り値 double	Usage player.z
Zengetter position	What does it do returns the player's current position. Can also be used to set a player's position	戻り値 Position3f	Usage player.position
Zengetter foodStats	What does it do returns the player's foodstats.	戻り値 IFoodStats	Usage player.foodStats
Zengetter bedLocation	What does it do returns the location of the player's bed.	戻り値 IBlockPos	Usage player.bedLocation
Zengetter fishHook	What does it do returns the player's fishingrod entity.	戻り値 [IEntityFishHook ](/Vanilla/Entities/IEntityFishHook /)	Usage player.fishHook
Zengetter foodStats	What does it do returns the player's foodstats.	戻り値 IFoodStats	Usage player.foodStats

ZenMethodsは、この場合、プレーヤーと他のものを行うためのものです。

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