Beginner poker players often start playing poker with play money instead of real money. I do not say you have to play with your salary because it is crazy and stupid, but playing with play money does not make any sense. Even if you do not know the poker rules it is ok to try poker and have fun for 1-2 hours with play money but then it gets boring.
The problem with play money is that you (and all others at the table) have no interest in winning while there is no money or price involved in the game. When play poker without money, you cannot lose any money either. This brings us to the conclusion that you do not risk anything and it does not matter if you play with a good strategy or you go all-in every hand.
If you only play on a $0.01/$0.02 cash game table, there is something to win and there will not be 3-4 players pushing all-in preflop like they do it on play money tables. On a play money table you just cannot develop your skills as the conditions are not even close to real money tables. Therefore I suggest you play on $0.01/$0.02 tables and not with play money.
There might be one play money poker game you should try. On several poker sites there are freeroll tournaments. The beginning of these tournaments is not better than play money games but later on when you are getting close to the money you can really learn a lot as the remaining players want to win too.
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By playing tournaments you can learn many different situations: pot odds calculations, all-in spots, blind stealing etc. If you can invest a little money, you can play for $1+$0.10 or $2+$0.20 buy-in tournaments and learn a lot from playing with a minimum investment.
You cannot play sitgo`s for free but you can find them for $1+$0.10 and $2+$0.20 and get experience fast. Sitgo`s are similar to tournaments but they are single table tournaments so they are perfect for practicing final table situations.