The aspirant gradually begins to feel that the Lord he worships is in the idol, in the hearts of all creatures and in the names and forms of all in this universe. He begins to feel His presence everywhere. -Swami Sivananda
A puja is a traditional ceremony, a Bhakti Yoga practice, a form of worship (or sitting near God). We cultivate a relationship with the Divine. Having a symbol helps concentrate the mind and turn it inwards.
Traditionally, we wear white, which represents purity. Donations of flowers, fruit or sweets are gratefully accepted, as are dedications.