Calculating Vo in the following problem
I get confused of what Vo is in such problems and how to calculate it 


That's fine. This way of drawing schematics might be new to you so at first it might be confusing. 

So go back to this first.







simulate this circuit &ndash; Schematic created using CircuitLab

Q: What is Vo?
Well, write KVL at the outermost mesh. They never lie to you. You'll find that Vo = VR2 - 2. Nothing more. In other words, you have to find first VR2 - then Vo (we call it output potential) will be under that voltage by 2V. If, say, V2 = 0 (i.e. R2 was connected between Vo and ground) then Vo is just VR2.