Help: Install Ubuntu Desktop 16 on VBox 5 hosted on CentOS 7.2?

I wanted to try Ubuntu Desktop - currently at V16...
Oracle Virtual Box was suggested as a way forward. I installed VBox 5.0 on my CentOS 7.2 (64bit) system. There is lots of disk space, but only 4 GB of memory.

I tried creating a guest system, but read some things that I didn't understand, and wanted some help getting started, at the very least.

So far I can start VBox to bring up its first GUI screen, but that's about it. I must add that I know very little about virtualization software.

Regards,
Lou.