Simple answer: Yes. Unfortunately it is not quite a simple as that, as if you want to enable parallelism, then you are obviously concerned about performance, and it is extremely tunable.
alter system set paralllel_automatic_tuning=true scope=spfile; then restart. This will have Oracle do what it thinks is best. There are many other parameters to set (e.g. parallel_execution_message_size) and you will need to experiment to find the best. Be careful with this; it is easy when you start out with parallel query to get carried away in benchmarking then discover in the "real world" a few queries fly but the overall throughput of the system actually decreases as some sessions are starved of CPU or the system is forced into swap. The documentation warns:
When concurrent users have too many
query server processes, memory
contention (paging), I/O contention,
or excessive context switching can
occur. This contention can reduce
system throughput to a level lower
than if parallel execution were not
So I strongly advise putting some limits in place, e.g. with resource consumer groups.
Also for any table you can do
ALTER TABLE table_name PARALLEL (DEGREE x); where x is a number, 4 or 8 might be good places to start.