Should I use Ubuntu Server or Desktop?

Hi
I more or less have the same setup as yoy with a simple dual core CPU and 4 gb ram and an old graphic card.

My plan is to install Open hab on it, so far a made install of ubunu 16 and java install.

But I dont understand how to install Open hab on it.

What shall i type in terminal, as I cant find openhab in the software download app.

Kind regards Alan