The esxtop command is available at the hypervisor level, so you need to connect to your ESXi hypervisor over Secure Shell (SSH) first, before you can issue the command.
Once you are logged-in, all you need to do is issue the esxtop command from the command line, as shown in the following screenshot:
The windows are automatically refreshed every 5 seconds so you can see what exactly is going on.
ESXTOP has a number of different views you can switch to:
- CPU view
- Interrupt view
- Memory view
- Network view
- Disk adapter view
- Disk device view
- VM disk view
- Power management
- vSAN
To switch to the different view, hit h to see what views are available and their corresponding shortcuts, as demonstrated in the following screenshot:
You also have an option to sort the items based on different metrics. Again, all the available commands are available from the help view, which you can switch to using the h key.
There are a lot of metrics available through ESXTOP, and Duncan Epping wrote a great series of blog posts about ESXTOP available at http://www.yellow-bricks.com/esxtop/.
You can also check the following article about interpreting ESXTOP counters at https://communities.vmware.com/docs/DOC-9279.