multi entries and 6 moths validity

i want to enter china this near future and in the next future, if i apply a multi entry with 6 months validity, is this possible, this coming near future, i only enter one, i just wanted to keep the multi entry for next visit and save the trouble for applying again.

what is 6 months validity?? does it means i can remain in there without exit for 6 months, and do not need to renew visa??