The only bit that might be confusing is the margin required to trade, as well as the maintenance margin. At the CME website you have a tab per contract where you can check the margin required (follow RealMoney's links). Brokers' requirements might be bigger, so check the contract specs at your broker at well. That margin amount is essentially cash that your broker will hold per trade, so as well as checking your pnl, check how your available funds fluctuate with the price.
[ NEVER mind the old S&P downgrade on US debt\sarcasm]