You gain the following benefits.
You learn the Light spell and can cast it without Material components. If you already know that cantrip, you learn a different Cleric cantrip of your choice. The spell's spellcasting ability is the ability increased by this feat.
When you cast Light, you can have the light from the spell be sunlight. Once you use this benefit, you can't use it again until you finish a Long Rest.
As a Bonus Action while within sunlight, you can expend one of your Hit Point Dice, roll the die, and regain a number of Hit Points equal to the roll. Once you use this benefit, you can't use it again until you finish a Short or Long Rest.