What does it mean when someone gets “tubes put in their ears”? where are they put? why?

I'll try to explain, because I've had tubes before.  In fact, I still have them.

For me, tubes were put in because of too many ear infections, and excessive water in my ear.  The tube helped drain the water out.  You can see A picture I have in a file.  The tubes can be put I believe in the ear drum.  They're put there to help drain water that has trouble getting out on its own.