gnuparallel

Dear friends,
Can someone instruct me how to use gnuparallel with an assigned number of cores? For example, I need to run i-tasser with 4 cores (gnuparallel). The only information I found after searching this board is to put "parallel -j 4". So should I run it with "-runstyle gnuparallel -j 4"? It doesn't seem work as expected.
Thank you very much.
Best,
Michael