Yeah error is what it is, you are trying to print a table. I believe you are looking for this particular post on data store which tells us that we need to do some JSONEncoding first though through the example script below.
local dataS = game:GetService('HttpService'):JSONEncode(userData) --Converts data to a a string
print('You are storing '..string.len(dataS)..' characters of data') --Prints 'You are storing x characters of data'.