P1(1,2,3) and P2(2,2,2)

Q1: Find a unitvector that points from P1 to P2. - A unitvector is a vector with length 1, right? But then what...?

Q2: A point M lies on the center on the line from P1 to P2. What is the position vector to M?

The sides of a parallellogram are a=2i-j+k and b=i+j

Q3: Find two vector that make up the diagonals. - I don't have a clue, which sides are a and b? And WHY! does my crappy book insist on writing everything with "i, i and k" thus making everything more difficult to read. (In HS we had fx: AB=[2,5,1]...)

Thanks for hints!