Calling a function on a table, and how does this code work?

function module:GetDatabase(sheet)
    local database = {}
    function database:PostAsync(key, value)
        return doPost(sheet, key, value)
    end
    function database:GetAsync(key)
        return doGet(sheet, key)
    end
    return database
end

So, from my understanding, whenever PostAsync() is called, doPost is returned, and whenever GetAsync() is called, doGet is returned? Am I correct in this understanding?

Also, functions are being called on the table? This code is confusing me for some reason.