Start by reading through the tutorial here: Pen Tool | Vectornator Learn iPad
Lots of useful tips (like double-tapping on the end node to stop drawing a curve).
There’s a file download at the top, but don’t start using it until after you’ve viewed the video at the bottom of the tutorial - that file is set up for the middle part of the video only. Navigate between the artboards by using the Layers panel (Layers icon on the top right), and tapping on the artboard names (they are the larger pale grey words). Start by reading the Instructions artboard and setting up Vectornator as it advises.
Use two fingers (two finger tips) to drag your view of the artboard around, or pinch those two finger tips in and out to change the zoom.
Then have a look at The Pen Tool
The 'Under the Hood" video is not necessary to using the Pen tool, but there is some other great Vectornator-specific advice here, including what the node colours mean, some of the gestures, and really useful controls such as changing the node types in the Styles panel (paintbrush icon in the top right).
There’s a link towards the bottom of that page to The Bézier Game, a great interactive web page that you can use to learn to use a vector Pen tool, even with your mouse on a desktop computer.
Note: the keyboard shortcuts in the game have Vectornator gesture alternatives - instead of Shift for direction snapping, start dragging the point and handle on Vectornator, then place another two finger tips somewhere on the canvas to start the direction snapping. Instead of Alt for “breaking” a pair of handles so they can each be manipulated separately, start dragging out the handle than place another sigle fingertip somewhere on the canvas.
Watch carefully when each page/shape first loads, there’s a quick preview tip/animation showing you how to solve each step. If you miss the first one on the opening page, refresh/reload the page.
You could also test the vector Pen tool at https://vectr.com/ although it is a little bit clunky. After drawing a curve with the Pen tool (tap for a sharp node, drag for a smooth node, Backspace to undo the last node drawn, Esc(ape) to stop drawing a curve). Double-click an existing curve to edit nodes, click on a node to get handles, hold Ctrl while manipulating a node control handle to “break” its connection with the partner handle.
If it helps, in Vectornator think of using the Pen tool as a virtual scissors with paper. Instead of cutting and turning the scissors to get a smooth curve, tap-and-drag to get a smooth node.
Instead of two sharp snips to get a sharp corner, just tap for a sharp corner.
To get curves coming together to make a sharp point (like a claw, curved fang, shark fin, or a very stylised wave logo), tap-and-drag to make the curve on one side of the shape, then hold down another finger tip on the canvas to break the curve and drag the other handle around to sharpen the tip (unfortunately, you’re not going to see the effect on the curve until you draw the next node along).
In Vectornator, Undo will undo the last node drawn while in Pen node (you can also use a double-finger tap on the canvas to undo - and a big thank you to the Procreate developers for introducing that convention to the iPad art apps).