Stats shows the CPU, memory, and network utilization, as well as a list of the processes for the container you are inspecting:

The graphs will automatically refresh if you leave the page open, and refreshing the page will zero the graphs and start afresh. This is because Portainer is receiving this information from the Docker API using the following command:

$ docker container stats cluster

Each time the page is refreshed, the command is started from scratch as Portainer currently does not poll Docker in the background to keep a record of statistics for each of the running containers.