Having trouble understanding Try Catch/ If else [on hold]

I'm sitting an exam in beginner level C# and I'm just going through some old papers to try get a grasp of thing. One of the tasks I have to do is read a section of code and comment on what's going on.I understand most of what is going on but im stuck on this section. Any help is greatly appreciated. Thanks.

Image of the code is linked below

https://i.stack.imgur.com/guW05.png