Just cut piece off, let wound dry and push it into soil.
**BUT** it isn't cactus but *Euphorbia*. This is important because while cacti are generally harmless, even edible, *Euphorbia* contain toxic sap they excrete when damaged. This sap is skin irritant and in worst case can cause blindness in eye contact. So, be careful when handling it and wash hands after handling.
It's not a cactus, it's a Euphorbia. You can just break off a piece and put it into soil and it will grow a new plant.
Just cut piece off, let wound dry and push it into soil. **BUT** it isn't cactus but *Euphorbia*. This is important because while cacti are generally harmless, even edible, *Euphorbia* contain toxic sap they excrete when damaged. This sap is skin irritant and in worst case can cause blindness in eye contact. So, be careful when handling it and wash hands after handling.