Some well-known file extensions used in VMware.
.VMDK -- These files are the actual hard disk of the virtual machine itself, and tend to be the largest file within the folder. You can consider the size of this file to be roughly equivalent to the size of either the disk itself (if you've chosen to use preallocated disks) or the size of the data currently stored on that disk (if you use growable disks).
.NVRAM -- Consider this file the BIOS of the virtual machine.
.VMX -- With typically one VMX file per folder, this file holds the configuration information for the virtual machine in a text format. Unlike almost all the other files you'll see, these files can be edited using any text editing program, a process that is actually required for some functionality that is not exposed in the GUI.
.VMXF -- This file, in XML format, includes additional information about the virtual machine if it has been added to a team. If a machine has been added to a team and then later removed, this file remains resident. This file can also be opened and read in a text editor.
.VMTM -- For virtual machines actively participating in a team, this file stores information about that team membership.
.VMEM -- These files, which contain a backup of the VMs paging file, are typically very small or non-existent when the virtual machine is powered off, but grow immediately to the size of configured RAM when the machine is powered on.
.VMSN and .VMSD -- When snapshots are created for a virtual machine, these files are created to host the state of the virtual machine. The VMSN file stores the running state of the machine, what you could consider the "delta" between the VMDK at the point of the snapshot and what has been processed up until the present time. The VMSD stores information and metadata about the snapshot itself.
.VMSS -- If you've suspected the state of your machine, this file contains the suspended state of that machine. These files typically only appear when virtual machines have been suspended.