Can I enable both opcache and memcache? Will it help? I have one dedicated server hosting magento 32gb ran 12 cores
As long as you are confident you will have sufficient memory available for both then yes there isn't any reason why you can't run both - they do completely different things. Memcached (note not memcache - memcached is newer and faster option) is key value store - so you are able to store a value to a key you define for later recall, and opcache is an opcode cache which pre compiles PHP scripts for faster operation when they are requested.
If you are actually talking about opcache which comes by default with PHP 5.5, then you should only be using this from CE 1.9.1 (soon to be released at the time of writing) and EE 1.14.1 (already released) both of which add support for PHP 5.5 and so make use of the extra performance of this PHP version. If you are using an earlier version then you can use APC instead which is another opcode cache and has the advantage of having a user key value store as well - opcache does not include this. For this reason, APC will probably continue to exist after opcache is established just with the user key value functionality. To confirm however, don't use the opcode cache functionality of both APC and opcache together - pick one or the other.