I would suggest a good place to dip your toe into real money
would be in low stakes sit and go's, some sites have $0.10 and $0.25
games which is a great place to learn a bit about real money poker without
losing a load of cash
I played the free tables for a good while and then I remember playing
my first ever real money table with a $5 buy in and I think it took me
all of 6 hands to lose it.
As someone else said you dont really learn anything playing on free tables
and can pick up some bad habits that will be hard to shift when you switch
to real money play
Another good way is to play on the lowest stake tables, there are $0.01-$0.02 tables where it would take you the best part of an hour to lose $1 and my advice would be when you do start playing for real money is remember two things,1/ play tight, play only premium starting hands, learn quickly that Ace rag will cost you a lot in the long run. 2/ be aggressive, get into the habit of raising rather than limping in or calling.
If you remember those two things you wont go far wrong