How memcached cache to memory server

[Nguyễn]

I'm using memcached on my web site, and I have a question about how
memcached cache to memory server if I'm using two or more server to
cache it?
Memcached function had a function addserver() I wonder how does it
cache to the next server, I guest that when memcached using full of
memory in the first server's memory so It's move to the next one or
memcached using another way to cache something like pooling?