How can I sort the nodes in order or by weight, or even once?

[iron-viper]

Hello. I'm sorry, but I really need your help. I have a week to read the code, and struggling with the task, but I can not understand how to do the following:
There's a schedule.
http://prntscr.com/755sr8
And I need to arrange such as node names in order, and that references to them were drawn. For example:
http://prntscr.com/755u1k
Followed by the name of the node.

Or, for example, I would like to add to the array data variable Level for each node. And it would be possible to put the node, depending on their Level
But I can not find how to do it and where you define how to display each node, and how to bring it to the link. Help me please. Thanks in advance.