The sliders basically customize how many npcs in the game are lesbian, bisexual, gay, pansexual or straight, putting it in the middle is the 'equivalent' part. Putting it more one direction will make them more likely to be whichever.
1st. Left [Straight] or Right [Any other sexuality I think]
2nd. Left [Bisexual] or Right [Pansexual]
3rd. Left [Gay] or Right [Lesbian]
Hope this helps