I'm having trouble with a Datastore for saving tables?

You can't save tables to datastores unfortunately, but you can save strings! To convert a table into a string, use HttpService:JSONEncode(). To convert that encoded table into a decoded one, use HttpService:JSONDecode(). Example:

local function SaveVariables(Player) 
    local http = game:GetService("HttpService")
    local plrStats = Player:WaitForChild("leaderstats")
    local Prestige = plrStats.Prestige
    local Level = plrStats.Level 
    local Exp = plrStats.Exp 
    local Guardian = Player:WaitForChild("Guardian") 
    local Outfit = Player:WaitForChild("Outfit")
    local Quest = Player:WaitForChild("Quest")
    local Skill_Folder = Player:WaitForChild("Skills")
    local Ab1 = Skill_Folder:WaitForChild("Skill1")
    local Ab2 = Skill_Folder:WaitForChild("Skill2")
    local Ab3 = Skill_Folder:WaitForChild("Skill3")
    local Ab4 = Skill_Folder:WaitForChild("Skill4")
    local Ab5 = Skill_Folder:WaitForChild("Skill5")

    local pos = 1

    local id = Player.UserId

    local PlayerTable = {}

    table.insert(PlayerTable, 1, Guardian.Value)
    table.insert(PlayerTable, 2, Level.Value)
    table.insert(PlayerTable, 3, Exp.Value)
    table.insert(PlayerTable, 4, Prestige.Value)
    table.insert(PlayerTable, 5, Outfit.Value)
    table.insert(PlayerTable, 6, Quest.Value)
    table.insert(PlayerTable, 7, Ab1.Value)
    table.insert(PlayerTable, 8, Ab2.Value)
    table.insert(PlayerTable, 9, Ab3.Value)
    table.insert(PlayerTable, 10, Ab4.Value)
    table.insert(PlayerTable, 11, Ab5.Value)

    local success, err = pcall(function() -- pcall just in case an error occurs
        PlayerStore:SetAsync(id, http:JSONEncode(PlayerTable)) -- Encode into a string, http:JSONDecode() to convert back into a table
    end)

    if not success then
        warn(err)
        return
    end

end