This gentle voice must have told the boy the significance of having altar and making offering be it small altar/offering or extensive one. They boy was happy because he is able to set up an altar even though it’s simple and minimal but he is given the opportunity to collect merits.
A proper altar holds images or representations of the Buddha's enlightened body, speech and mind which serves as reminders of the goal of Buddhist practice -- to develop these qualities in oneself so as to be able to fully benefit all sentient beings. The reason for setting up an altar is not for fame, for showing off wealth, or to increase pride, but rather it is to reduce one's mental afflictions and to seek the ability to help all sentient beings.
In term of the offering, there is no limitation to what can be offered, and there are many levels of offering. In general, one can offer any pleasing object, particularly objects pleasing to the five senses -- form, sound, smell, taste, and touch.
In the Tibetan Buddhist tradition it is customary to offer seven bowls of water which represent the seven limbs of prayer -- prostrating, offering, confession, rejoicing in the good qualities of oneself and others, requesting the Buddhas to remain in this world, beseeching them to teach others, and dedicating the merits.
Flowers, candles or butter lamps, and incense are also commonly offered. It is customary to offer a part of every meal on the altar before eating and a portion of tea before drinking.
The things that should be offered should be clean, new and pleasing. . . . only the best part, fresh, and clean -- never old, leftover, or spoiled food.
It is best to offer things that you already have or can obtain without difficulty. Don't think that you have to deceive others in order to get offering materials -- they should not come from stealing, cheating or hurting others in any way. Rather, they should be honestly obtained. In fact, it is better not to offer things that were obtained in even a slightly negative way.
As you make offerings, think that what you are offering is in nature your own good qualities and your practice, although it appears in the form of external offering objects. These external offerings should not be imagined as limited to the actual objects on the altar, but should be seen as vast in number, as extensive as space.
Offer food with the wish that all beings be relieved of hunger, and offer water with the wish that all beings be relieved of thirst.
It is important to think that the deities accept the offerings, enjoy them and are pleased. Think that by making these offerings all beings are purified of their negative qualities and their thirst for knowledge of the ultimate nature of reality is satisfied.
The purpose of making offerings is to accumulate merit and in particular to develop and increase the mind of generosity and to reduce stinginess and miserliness. By making offerings you also create the causes for the future results of becoming wealthy and becoming naturally and spontaneously generous.