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Type it in to terminal :)
A fusion drive is basically a cache between your SSD and your HDD. It's powered by a special driver that manages the movement of data between the two. So if CPU power is your top priority, you will gain a bit by splitting it, but only a bit.
Fusion drives work well with small files, but less well with big ones, so power users using big files are better off avoiding them as there will be annoying starts and stops as the system is moves big chunks of data to accommodate new files. Also fusion drives use HFS+ which increases the risk of corrupted files, and because there are two drives combined your risk of a drive failure increases by 100% so you should always back up if you do use them.
mkdir hammerTime
chmod 500 hammerTime
cd hammerTime
touch this
etc.