The simplest straight ahead method is the boolean add and subtract tools in the toolbar at the upper right in the default Affinity Designer Configuration.
This is a destructive workflow (one in which once an action is taken, it cannot be easily modified or undone later upon file re-open) as it directly edits the shapes or paths.
@user287001 suggests looking for a non-destructive method - turns out this is dead simple.
Many thanks to @Stéphane Bura for pointing this out in the comments - there is already an existing non-destructive boolean workflow in Affinity Designer - what I initially showed (and will leave up after this step) is a minorly-clunky workaround - the actual in-built non-destructive boolean is super-simple and elegant.
Use the same boolean subtraction method I already outlined above, only as you click the subtraction button, hold the Alt(PC) or Option(Mac) key down.
This creates nice compound shapes which you can easily see and manage in the Layers Studio - exactly what the doctor ordered!
Oh for those who might wonder - this also allows for nesting of this non-destructively - that is, compounds within compounds - just remember to hold Alt or Option when you use any boolean and you're in business.
Here I made a non-destructive boolean union of the base bite circle and some teeth (more ellipses rotated around the centre of the bite circle) by holding Alt or Option when clicking the boolean union button, then once I had that compound in front of the base cookie circle, again holding Alt or Option when I clicked the boolean subtraction, and here we get the whole composition non-destructively, so you can keep editing for example tooth positions or shapes later on if you wish.
My older workaround before knowing about the Option approach: same as previous but with one extra step: do the same boolean with the same cutter shape to a rectangle large enough to enclose your target positive shape, and once the cut's been made, put your target shape inside that in the layer studio, making it a clipping mask.
The last step is then selecting the fill and stroke of the container (which was a cyan rectangle in my example) and setting it to "none" - the red slash through white symbol in the colour picker.
Your cookie is still complete, live and editable, as is its alignment with its cutter, and the cutter shape is too - so this is a non-destructive workfow in which maximal flexibility is maintained.
To demonstrate that, here I've changed the clipping shape's curves to add some rough teethmarks to the bite, but if you look over at the layers studio you can see that the cookie is still a simple circle.
Hope this helps.