Hi Yves
Guess you're looking about this steps:
1) On the left panel choose "Host and Cluster"
2) select the host with your Vms you want automatically power on
3) On the right panel click on "Configure"
4) Then on the "Virtual Machine" menù choose "VM Startup/Shutdown"
5) And then click on "Edit" to configure your VMs to auto startup and or shutdown
Hope this can help you
Enjoy whit VmWare
Maurizio