You gain the following benefits.
You always have the Fog Cloud spell prepared. You can cast it without a spell slot, and you must finish a Long Rest before you can cast it in this way again. You can also cast it using spell slots you have of the appropriate level. Your spellcasting ability for the spell is the ability increased by this feat.
Whenever you cast Fog Cloud, nonmagical flames in the spell's Sphere are extinguished, and creatures other than you and your allies have their Speed reduced by 5 feet while in the spell's Sphere.