One entry in a model can be Marked at any time. If, for example you were working in one part of the model and you wanted to go off somewhere else temporarily, mark the present entry and then use Jump to mark to return to the entry you marked. The Mark, meanwhile, travels to the place you just came from, giving you a neat way of diving back and forth between areas of focus.
(Opening two, or more, windows on that same model provides an alternative way of focusing on different parts of the model. Whether you use Mark and Jump, or Split window rather depends on what you're using BrainStorm for.)
The Mark can also act as a source for Retrieve entry or the destination for Throw entry(ies) operations. These move entries from one part of the model to another.
(Again, using multiple open windows, you may achieve similar results by dragging and dropping. It rather depends if you prefer the mouse or the keyboard.)
One other thing. If a list ends with a series of blank entries, they will automatically be removed, when moving to another part of the model. If one of these blank entries is Marked, then this will become the last entry in the list.Use: