VMA stands for vSphere Management Assistant. It's a virtual appliance that allows administrators and developers to run scripts and agents to manage ESXi hosts and vCenter Server systems.

You can download it here: https://www.vmware.com/support/developer/vima/

After you deploy the OVF template into your environment you can SSH into it and get started.

VMware has included all their esxcfg commands but one command is very usfull it's vifp (vi fast pass), which allows you to stored credentials for ESXi hosts so you don’t have to type them every time you run a command or script.  
So first we add our vCenter and ESXi hosts:
vifp addserver vcenter_or_esxi_fqdn
To verify what servers have been added run:
vifp listservers

You can also add the vMA to active directory so you don’t have to store the passwords in vifp.  This can be accomplished with the domainjoin-cli command:
sudo domainjoin-cli join domain_name domain_admin_user

That's it lets test if we can run commands again ESXi hosts from our VMA. For example list our vmnics:

vicfg-nics -l --vihost esxi