I don't understand this part of an English text.

Could you explain me please what is described by the following sentences? They are from Baldwin Spencer's and Francis James Gillen's book entitled The Northern Tribes of Central Australia, wirtten in 1904, from a description of an aboriginal ceremony. "After decorating the boy the elder brother cut a limb from a tree, and, slanting it against the latter, left the boy sitting straddle-legged across it. He himself went on to the camp and told the mother to go out and see the boy. Accordingly she went, carrying with her a supply of sugar-bags and lilies, gathered for the purpose. After rubbing the boy all over with red ochre she took him off the branch and gave him the food..." It isn't clear for me what happens to the branch of tree. What does the boy do with it and with his brother?