Understanding the output of boosting




I ran the boosting algorithm on the iris dataset and got some output which I am not entirely clear about:

1.What does the loss signify?
2.I think there are three nodes getting generated here,so are the probabilities at each node?
3.What does the o/p beside 1),2) and 3) signify.
I am basically trying to understand the output so can somebody please help me with it?