English: The red means two things: if there is only one red line on the frame, it means "This line is the radius that the just constructed circle has." If there are two or more red lines on the frame, then it means "These radii must be equal to each other."
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.