There are two things you should check in order to enable the snapping you need

For the action you need to perform, check the snapping menu on the right side of the upper toolbar, with the magnet icon 🧲 You can activate/deactivate it, but also open the snapping settings panel in which you can choose the behaviour of the snapping. Here you have a more detailed description Snapping on Affinity.help

You may need to check also the curve snapping if you need dinamic guides during curves manipulation. You can find the setting in the upper context toolbar while using the Pen tool or the Node tool. Also for these settings you can refer to the official guide: Curve snapping on Affinity.help