Hi Peter, it's 16.04, not 16.4 - this numbering system applies to Ubuntu, but not necessarily to other Linux Distros.
Mark Shuttleworth (owner of Canonical, which distribute Ubuntu) uses a numbering system where the first two digits are for the year, the 2 digits following the fullstop are for the month. So 16.04 was released in April 2016.
Their method of delivery is called a point release (alternative is called a rolling release), and they release a new point release every six months. Then, every even-numbered year, they release, in April, an LTS (long-term support), which has a shelf life of 5 years for support in terms of updates and fixes, security modifications &c. The point releases in between have a shelf life of only 9 months.
To further, confuse, he/they use a two-word codename, where the first word is an adjective, and the second either a South African animal, or other exotic animal or a mythical creature.
So starting with the 2014 LTS:
Ubuntu 14.04 'Trusty Tahr' LTS - support ends April 2019. A Tahr is a Himalayan deer.
Skipping to 2016:
Ubuntu 16.04 'Xenial Xerus' LTS - released April 2016, end of support is April 2021. Xenial means hospitable and a xerus is an African ground squirrel not unlike a meerkat.
Ubuntu 16.10 'Yakkety Yak' - released October 2016, support ended July 2017.
Ubuntu 17.04 'Zesty Zapus' - released April 2017, support ends 20th January coming up (all releases are on the 20th of the month). A zapus is genus of North American jumping mouse.
Ubuntu 17.10 'Artful Aardvark' - released last October 20th, support ends 20th July this year.
Next release will be an LTS on 20th April 2018, codenamed 'Bionic Beaver'.
Now all of the above might seem as exciting as watching the paint dry and I reckon the paint would win.
But it is handy to understand what you are downloading and installing eg Do I want this fella when it only has a 9 month life, or do I go long-term?
DE is for Desktop Environment, and this article explains better than I:
https://renewablepcs.wordpress.com/about-linux/kde-gnome-or-xfce/
In Ubuntu 16.04, you will be using one of :
Each has a different look and feel, menus and launchers and system trays are placed differently. My 16.04.3 Xenial Unity looks like this:
That is the Unity Launcher on the left, and at the top where my mouse cursor/pointer is is The Dash, where you can search for and launch Applications.
If yours is like this, then we know where your recalcitrant icons are.
If you have a "Panel" on the bottom or top of the screen, with the word "Menu" at the left, you are likely on MATE.
If you have a squarish-looking 9 dots, and the word Activities, then GNOME.
So the sooner we can find these things out, the sooner we can help more, and that is where I mentioned the command at Terminal
... whose output you can see in my Spoiler, that is, after you install inxi.
My spoiler included
Hope this all makes sense and keep smilin'
Cheers
Wizard
BTW - click the screenshot (picture) and it will increase in size, click it again and it restores to usual, this is called a toggle effect.
Edited - added BTW