2. To learn how to construct perpendicular lines through any given point. (point on the line or outside the line)

3. To learn how to how to bisect lines at right angles or to construct a perpendicular bisector

4.To learn how to construct angles using ruler and compass. (60˚, 120˚)

5. To learn how to bisect angles. 

6.To apply the nowledge gained to construct (30˚, 90˚, 45˚ , 75˚, 105˚, 135˚)  

Why did Euclid do it this way? 

Why didn't Euclid just measure things with a ruler and calculate lengths?
 For example, one of the basic constructions is bisecting a line (dividing it into two equal parts). 
Why not just measure it with a ruler and divide by two? 
 
 One theory is the the Greeks could not easily do arithmetic. 

They had only whole numbers, no zero, and no negative numbers. 
This meant they could not for example divide 5 by 2 and get 2.5, because 2.5 is not a whole number - the only kind they had. 
Also, their numbers did not use a positional system like ours, with units, tens , hundreds etc, but more like the Roman numerals. In short, it was quite difficult to do useful arithmetic. 
 
 So, faced with the problem of finding the midpoint of a line, it was very difficult to do the obvious - measure it and divide by two. 
This led to the constructions using compass and straightedge or ruler. 
It is also why the straightedge has no markings. 
It is definitely not a graduated ruler, but simply a pencil guide for making straight lines.
 Euclid and the Greeks solved problems graphically, by drawing shapes instead of using arithmetic.