Points tab
Move up, down, left, right
These buttons move selected points by 1px, or 10px if you hold Shift. If you hold Alt when you click them, the tangents that belong to the points will be 'left behind' instead of moved with the points.
Bear in mind that move, align, distribute and snap to pixels functions will behave parallel to the X and Y axes of whichever Space is active.
Align and Distribute
The Align and Distribute functions all move selected elements into a line, and correspond to panels found in Creative Cloud applications. They work per path - you cannot align or distribute elements from different paths.
Mirror points on the X or Y axis
The mirror buttons require an open path with either the first or last point selected. They will then mirror the shape around that point.
Toggle open / closed at selected points
Use this button to quickly open a closed path between two points. Select two consecutive points, click the button, and the path will be opened at that segment.
Unlike the similar button in the Paths tab, this button opens the path between selected points, instead of always doing so at it's first vertex. This will alter which point is the first vertex.
If you select a path that is already open and click this button, it will simply be closed.
Break path
This button will break a path into two or more paths, at the selected points. Penpal generates new path objects in your layer, and turns off the old one.
If you select only one point on a closed path and click this button, it works a little differently. Instead of generating new paths, Penpal will split the path at the selected point, so that you have an open path which looks the same as the closed one (but has an extra point). This is essentially the same as using the Scissors tool in Adobe Illustrator.
If you break a path and then use Undo, you'll need to reload your path in Penpal before continuing.
Set first vertex
This is exactly the same as After Effect’s native Set First Vertex operation, and will set the selected point to be the first vertex.
Snap to pixels
By default, this button will shift all selected points so that they are located on the nearest whole pixel. If you click the button that pops up below it, you can change the default snap value.
This snapping is relative to the active Space, so it might only snap to the actual composition pixels if you are in Comp space.
If you hold Alt while you click the snap button, tangents of selected points will also be snapped, as independent elements to the points.
Hover over the button and click the gear icon to set the value that the Snap To Pixels button applies.