Simply put, VESA is a standard and it is very easy to understand. When you see VESA 100 for example this means that the mounting holes on the rear of your TV are 100mm apart vertically and horizontally.

If however you see two numbers such as VESA 600x200, this means that the distance between the holes is 600mm horizontally and 200mm vertically.

Very simple! 99% of TV's conform to VESA but if your TV does not then please look for UNIVERSAL or Mis-Fit adapter plates. The plates are rare on eBay but a quick Google search reveals some stockists.

Thanks.