net long exposure

what does this mean? if i take a long position on a futures contract, shouldnt the exposure be zero since the trade is guaranteed by the clearinghouse?

Your net long position in futures contracts would probably be something like your longs -shorts over all expiration dates. The only thing the clearinghouse does for you is take away credit risk, but you can surely be long or short the underlier.

so it means that we have more exposure on the long positions than on the short positions we hold?

what it comes down to that you will make money if underlying goes up and lose money if underlying goes down.