Lol. The prayer doesn't show who does black magic.
Salatul Istikharah is offered to seek Allah Ta'lah's guidance in any matter where you cannot be sure which is the best course of action to take.
You first perform two rak'ahs of sunnah or nafl salah, with the intention of making Istikharah, then you say a special dua.
Once you have made Istikhrah, Allah Ta'lah swt may cause you to keep firm to your choice or to change your mind. Allah Ta'lah swt knows best. After you have gone through with whatever decision you have finally made, you should trust that Allah Ta'lah swt led you to do what is best, and should have no regret.
Also again, read Suratun Nas (114) and Sarantul Falag (113) to seek refuge from the mischeif of the sneaking whisperer (who blow on knots or practice black magic.)