The keyboard shortcuts aren't like most vector editors, since Scratch can't detect alt, shift, and ctrl keys and right-clicking, but it should have the same general idea: Click off of the shape to move it by dragging the background. (This is a bit strange, but since there is only one object, it doesn't really matter.) Click back on the line of the shape to edit the nodes. Click on a node to select it. Press Z while a node is selected to switch it between curved and pointed. Press X to delete it if the shape has more than two nodes. Use S to toggle an open/closed shape.
This might be the best vector editor on Scratch! I already knew all of the math do do this, so it really wasn't that hard. Figuring out how to place a node without changing the shape was a bit tricky, so at least give this a heart and star for the small bit of effort it took to make this project. I would recommend TurboWarp for more than 20 nodes: https://turbowarp.org/877712253?hqpen If you haven't used a vector editor before, (I don't know why) then you click on the shape when it's selected to add a node and drag the square things to change the trajectory of the line the node determines. The nodes are the dots and are also draggable. Please do NOT report bugs.