There are a number of glues you can use on balsa: PVA, superglue or balsa cement (UHU HART).
PVA: time to adjust
Run a good quality PVA across the gluing edge and hold the parts firmly in place until they hold. PVA takes a few hours to dry completely, so you have time to reposition the parts if you need to.
Superglue: quick builds
Superglue makes for quicker builds. Apply it along the edge, hold the parts in place, then spray with a superglue accelerator such as Zip Kicker, which sets the bond instantly. Superglue suits parts with a small gluing area, such as the end of a rod.
Balsa cement (UHU HART)
Apply a thin layer of UHU HART to one side, place the parts together straight away and hold them in place.
For hard, enclosed surfaces, apply a thin layer to both sides and let it dry. Then apply again to one side, place the parts together and hold them in place.
What you need
- Balsa
- One of: PVA, superglue with Zip Kicker, or UHU HART
Which glue for which material
The adhesives guide on model.shop tells you which glue to use when you are sticking two different materials together.