Here you add the vectors together keeping the angle, so draw them from head(u) to toe(v) and look at them. If you did it correctly it should look like a roof or a ^ with a bigger angle. Then, draw a line from the start point of u to the end point of v. The new line is your It should now look like a triangle
In you're just adding the total magnitude of the two vectors, so just draw the magnitude of vector v, and then continuing in a straight line draw the magnitude of vector u. Just add the vectors together in a straight line and call it . Done correctly this would just look like a straight line.
Look at what you drew, analyze it, and understand it's an exercise to get you to see why the triangle identity works. They just want you to draw it so that you can also conceptualize it in your mind. The idea is you'll learn the math language more intuitively and it's an opportunity to see why math works the way it does. Good luck!
The most fundamental concept here is "a straight line is the shortest distance between two points". The direct line from the base of u to the tip of v is a single straight line which is thus shorter than going from the base of u to the tip of u and then to the tip of v.