To create an arc you can either enter three points (By 3 points, see Point definition) or enter a radius and the two tangent lines at the arc's ends (Fillet curves).
It is important to note that when creating an arc, new points are also being created (if existing ones are not being used).
An arc that begins and ends at the same point (i.e. where the first and third points are the same) will be created as a circle. An arc will always include the second point that is entered, though this one is only used as a reference and, if it is not an existing point, is automatically erased when the arc is created.
The Undo option undoes the creation of the last point (if it is a new one). It is possible to continue undoing all the way back to the first point.
The Fillet curves option lets you input a radius and select two lines that share one common point. An arc will then be created and the two lines will be modified to be tangent and continuous with this new arc.
To convert one arc to another one with the same center and in the same plane but with a complementary angle, the Swap arc command can be used (see Swap arc).