Use "two thousand and ten"; "twenty-ten" is also understandable but sounds like shorthand.
For a hundred years ago, you 'd also use "nineteen hundred and ten" or "nineteen-ten".
For talking about whole decades, just use "twenty----" eg twenty-twenties, twenty-thirties etc. We still haven't agreed on how to describe the first 2 decades of a century yet, in English. (Twenty-Teens??) ;)