string expected, got table, what does that mean?

This is how you properly create leaderstats. Not sure if this is what you were referring to since your question was vague.

--CODE

--DO NOT FORGET TO DEFINE WHO THE PLAYER IS!!

local leaderstats = Instance.new("Folder", player)
leaderstats.Name = "leaderstats"

That means you passed or put in table instead of string -- table is something like (cat, dog, lizard), containing several values. String is something typed in words - like "Hello, I am Lukas".

You may accidentally used wrong variable, which contains table instead of string. If you requested it from data store it will return it in table form, that means you will need to access it in that way:

for i, v in pairs(table) do
    -- table is {cat, dog, lizard}
    print(v)
end

-- output - cat   dog   lizard