I mannaged to solve my own problem.
In case someone will find this answer usefull i will post it.
Frist i created 27 variables which contain description text.I called them Description1-Description27.
Each Description for one Node.
Then I created variable with expression to make string from word Description and NodeID number.
Change its value depending on node selection.
I used this statement to test which node is selected and what Description to show.
It worked perfectly.