What are the constructible angles ?
Wikipidia sais:
The only angles of finite order that may be constructed starting with two points are those whose order is either a power of two, or a product of a power of two and a set of distinct Fermat primes.
I don't understand the exact meaning of this, does it say that an angle is constructible if and only if it is a power of two or a product of a power and $?$ (this part I didn't understand either)
It means an angle is constructible if and only if its order is either a power of two, or a power of two times a set of Fermat primes. For example, 10 = 2*5, and 2 is a power of two and 5 is a fermat prime, thus you can make an angle of 360/10 = 36 degrees. but 40 degrees = 360/9 cannot be constructed, because 9=3*3, and 3, 3 are not distinct.