The Point by Angle tool allows you to create a point which is positioned based on an angle that you define. Your
initial touch defines the vertex of the angle. You then drag and use the Mark Button

to define the two endpoints of the angle. This is different from how angles are usually defined in
Doodleback (it’s usually endpoint-vertex-endpoint), but the reason is that the two endpoints actually define the line on which the point will lie so
really what you’re defining is a vertex and then a guide segment. Here’s an example:

You can move the point along that line either freely or in angle increments. Also, when defining the angle, you
can use the Drag Constraint button

to horizontally or vertically align one of the points with another.