Secular use this time to provide necessities, such as food, robes, medicine, candles, incense sticks, etc.. that monks can use during those three months.
Candles were very useful and a source of light at night, which is why the villagers gave the beeswax to make candles.
It has become a tradition to offer lanterns monasteries during the rainy season.
Dhamma: that word has many meanings in Buddhism. In this case (Buddhism Teravada) it refers to the Buddha's teachings contained in the Tipitaka, the Pali scriptures.