how can i start blender 2.8 in ubuntu 18.04 Ive downloaded blender 2.8 and extracted files to a suitable folder. But when i double click on the 'blender' program nothing happens.
I used the same procedure with blender 2.79b and that works just fine.
I need 2.80 as i'm having trouble with mhx2 import in 2.79b - the addon is enabled but nothing appears under file import, and my understanding is that mhx2 was updated for blender 2.80 and no longer works with 2.79b, and i can't seem to find earlier version....
/gary
PS it wiuld be helpful if tags could be selected from dropdown nenu or something  as i dont know all the names
The version you downloaded might not be configured for your distribution. To see if there were some error messages you can open a Terminal window in the folder you extracted blender to by right clicking in the file browser and choosing "Open in Terminal". Then run the program by typing "./blender" (or whatever the program file is called), hit enter and see if there are any error messages.

However I would advise to install Blender from another source that has been tested with your OS instead. There is a PPA for newer versions of Blender maintained by Thomas Schiex: https://launchpad.net/~thomas-schiex/+archive/ubuntu/blender
If you don't mind using the newer development version of Blender (2.81) it might be what you want. You can add a PPA to your system by following the instruction close to the bottom of the linked page or through the Synaptic package manager.