Create some nodes using the pen found in the tools. Create a basic open path or closed path and then go to the Affinity Photo node tool (found beneath the pen). You can also just use a shape that has been converted to curves.
As soon as you select it, you will see a number of options along the control bar such as 'mode' and 'actions'.
Select a point and you will see it suddenly becomes blue, you can also drag over multiple points and select those as well. The point can be a smart (curved) point or a smooth point or a sharp point (corner point in Illustrator). You convert between them by clicking the smooth or sharp buttons in the mode. The smart offers the best curve for the path.
You can also hold down a variety of keys such as shift to constrain the movement of the handles. You can hold down the control key to freeze the control points but allow the main point to move. You can hold down the alt / option key to move the control points independent (there is an in and out control handle, you can then move the in or the out separately).
You can also select a point or multiple points and actions and break curve which will then break the curve at that point leading to separate open paths. With a point selected, you can also click the close curve to close the start and end points for a curve (especially useful after breaking the curves).
You can select two or more open paths and then use the join command to join them into one path (it draws a straight line from the end point to the start point of the other curve.
The reverse option switch the points order.