Okay, so imagine you had a toy car and you want to let your friend play with it for a while. But you also want to make sure they will give it back to you when they are done playing with it. That's kind of like what a bai sema is.
In some cultures, people use bai sema as markers to show where important places or sacred sites are located. Bai sema are usually round or rectangular stones that are placed in a line or circle. They are kind of like signs or flags.
When people put a bai sema in a certain spot, they are saying something like, "This is an important place. Please respect it and don't damage it." It's a way to mark a location as special or sacred.
Just like with your toy car, a bai sema also tells people who have borrowed or used the space that they need to return it to its original condition, like putting things back where they found them, or not littering.
So bai sema is basically a special marker that tells people where important places or things are, and reminds them to treat them with respect and care.