Pcb
can handle arcs of any angular extent, but when you
create an arc with the Arc tool, it will
be a quarter circle (this means they always bend a right angle). Arcs are very similar
to lines otherwise. They are created on the active layer and have the same thickness
that new lines will have. The various clicks for creating lines work pretty much the
same way for creating arcs.
In order to make the arc curve in the desired direction, drag the mouse along
the tangent line from the starting position towards the end position. If the grid is
too coarse, it may not be possible to distinguish whether you've moved over then up,
or up then over, so if you can't seem to make the arc go in the direction you want, try pressing
the Shift key while drawing the arc. Decreasing the grid spacing may also help.
Alternatively you can draw the wrong arc, then
rotate and move it where you want. Like the Line tool, after an arc is drawn a new
starting point is established at the end point.
Whenever a starting point is established by either the Line or Arc tools it will be retained if you switch directly between the tools (e.g. F2 key for Lines, F8 key for Arcs. Arcs can either touch or clear polygons just like lines do. Of course connection searches, undo and all the other features you'd expect work with arcs too.