You can find it in the tools along with the panel in the window menu and Astute graphics category.
To create rounded etc corners from the selected shapes.
On paths, if you want to apply it to type then you will need to go to the object menu and expand.
You can use the tool to individually modify the points of a vector such as a rectangle, open path, star etc You can manipulate the design with the curve annotation. You can set the type such as negative etc via the panel. Go from one point to the next or perhaps skip some of the points on a path
You can select the shape or just some of the points The panel works on the selected and you change the current settings for all the points, though if a point is outside of the range, it will be ignored (there appears to be no override). If you can't see anything on the panel, you occasionally have to re-activate it by clicking it and all the options will appear. You can set the radius, you can also set three different radio types and they are all different (true, standard and squircular) as well as three types of corners (regular, negative, chamfered) and to apply, just click the apply to selected. There is also a right side menu that allows for the removal of the effect as well as removal of selected etc (basically freezes it), there is no expand command but that can be done via the object menu and expand. If you remove, you can bring them back via the convert commands in the same menu.
While the tool is active, interactive options are available on the shape so you can also modify the radius on the shape itself.