Anyone know anything about the ChatSystem? I don't understand it at all..

Make a ServerScript in ServerScriptService and put this code in (change values as nessacary shown in the comments!)

local ChatService = require(game:GetService("ServerScriptService"):WaitForChild("ChatServiceRunner"):WaitForChild("ChatService"))
local groupId = 000000 -- Group ID here

game.Players.PlayerAdded:Connect(function(player)
    while not ChatService:GetSpeaker(player.Name) do wait() end -- Wait till the player's speaker (thing that allows it to chat) exists
    local speaker = ChatService:GetSpeaker(player.Name)
    if player:GetRoleInGroup(groupId) == "Guest" then return end -- Remove this if you want it to do say [Guest] if they player isn't in the group
    speaker:SetExtraData("Tags", {{TagText = player:GetRoleInGroup(groupId), TagColor = Color3.fromRGB(0, 255, 0)}})
    -- Change the values in Color3.fromRGB() for a different tag color
end)

For the whisper chat (do this pre-runtime)(anytime i bold a name you must write it just like that): 1. Insert a Folder into Chat called "ChatModules" 2. Insert a BoolValue into **ChatModules** called "InsertDefaultModules" and set it's value to true 3. Insert a ModuleScript into ChatModules and put this in the module (make sure to make the remote event that the script references!)

local sendPopup = game.ReplicatedStorage.SendWhisperChatPopup -- Reference a remote event
local TextService = game:GetService("TextService") -- Filter messages so they have no swears

local function Run(ChatService)
    local function filterMessage(message, speaker, reciever)
        local filteringResult = TextService:FilterStringAsync(message, speaker.UserId)
        if not game.Chat:CanUserChatAsync(speaker.UserId) or not game.Chat:CanUserChatAsync(reciever.UserId) or not game.Chat:CanUsersChatAsync(speaker.UserId, reciever.UserId) then
            -- Player(s) cannot chat, send back a DONT SEND MESSAGE prompt
            return 0
        end
        return filteringResult:GetChatForUserAsync(reciever.UserId)
    end

    local function whisperCheck(speakerName, message, channelName)
        if string.sub(channelName, 1, 2) == "To" then -- If whisper channel then
            local otherPlayer = game.Players:FindFirstChild(string.sub(channelName, 4)) -- Get the other player
            local speakerPlayer = game.Players:FindFirstChild(speakerName) -- Get the player who said something
            local newMessage
            local succ, err = pcall(function() newMessage = filterMessage(message, speakerPlayer, otherPlayer) end)
            if newMessage == 0 then
                -- Player can't chat
                sendPopup:FireClient(speakerPlayer, "Note", "One of you can't chat!")
                return true
            end
            if err then
                sendPopup:FireClient(speakerPlayer, "Filtering failure", err)
                return true
            end
            -- We can send message
            sendPopup:FireClient(otherPlayer, speakerName, newMessage)
            return true
        end
        return false
    end

    ChatService:RegisterProcessCommandsFunction("whisperCheck", whisperCheck)
end

return Run

1. Next, make a ScreenGui in StarterGui
2. Insert a LocalScript into the ScreenGui and put this in it (remember to reference the remote event you made earlier where you need to!)

local inSession = false -- if another chat is on screen
local START_POS = UDim2.new(0, -300, 1, 0)
local END_POS = UDim2.new(0, 0, 1, 0)
local SIZE = UDim2.new(0, 200, 0, 50)
local ANCHOR_POINT = Vector2.new(0,1)
local TIME = 0.2
local doneEvent = Instance.new("BindableEvent", script.Parent)

local function showLabel(speakerName, message)
    if not inSession then
        inSession = true
        local label = Instance.new("TextLabel", script.Parent)
        label.Name = "WhisperBox"
        label.BackgroundColor3 = Color3.fromRGB(0,0,0)
        label.BackgroundTransparency = 0.5
        label.BorderSizePixel = 0
        label.Font = Enum.Font.SciFi
        label.TextScaled = true
        label.TextColor3 = Color3.fromRGB(255,255,255)
        label.AnchorPoint = ANCHOR_POINT
        label.Position = START_POS
        label.Size = SIZE
        label.Text = speakerName..": "..message
        label:TweenPosition(END_POS, Enum.EasingDirection.Out, Enum.EasingStyle.Quad, TIME, true)
        wait(5 + TIME)
        label:TweenPosition(START_POS, Enum.EasingDirection.Out, Enum.EasingStyle.Quad, TIME, true)
        wait(TIME)
        label:Destroy()
        label = nil
        inSession = false
        doneEvent:Fire()
    else
        doneEvent.Event:Wait()
        showLabel(speakerName, message)
    end
end

game.ReplicatedStorage.SendWhisperChatPopup.OnClientEvent:Connect(showLabel)

I tested it and it works!