This is a ceremony which follows mangala arati, the first worship of the day. Tulasi is a sacred plant which is very dear to the Lord, and worship of Tulasi-devi is most beneficial. Tulasi-arati is performed like this: The devotees sing prayers to Srimati Tulasi-devi (the Tulasi Pranama, q.v.) while one devotee offers her arati with incense, ghee lamp, and flowers. When the song is finished, the assembled Vaishnavas circumambulate Tulasi-devi and offer her water by pouring some drops at her root.
The following passage from the Skanda Purana gives a glimpse of the unlimited glories of Tulasi-devi:
Tulasi is auspicious in all respects. Simply by seeing, simply by touching, simply by remembering, simply by praying to, simply by bowing before, simply by hearing about or simply by sowing this tree, there is always auspiciousness. Anyone who comes in touch with the tulasi tree in the above-mentioned ways lives eternally in the Vaikuntha [spiritual] world.
(See also: mangala arati, Eight Aratis.)