I'm trying to understand Example 10.11.1 on page 225 of the book *"An introduction to quiver representations"* by Harm Derksen and Jerzy Weyman (see the attached screenshot below) 

[![enter image description here][1]][1]

I want to understand the line underlined in red. 

>How does the choice of vectors $(\lambda,\mu,\nu)$ being $(1,0,0),(0,1,0),(0,0,1)$ give us a basis for the weight space $\mathrm{SI}(Q,\beta)_{\langle(2,3,2),\cdot\rangle}$?


  [1]: https://i.sstatic.net/ivmyt.png