Loading opencpn

I have recently installed ubuntu 12.04 and I am reinstalling Opencpn. At firt it would not install so I went to the Opencpn webpage and read the instructions (when all ele fails read the instructions...right?). I installed Synaptic and then I followed the commands to go to the terminal and type sudo gdebi <downloaded_opencpn_file.deb>. This didn't work so I followed the next instruction and pasted into the terminal "sudo apt-get install libwxgtk2.8-0 libwxbase2.8-0 wx-common libglu1-mesa libgl1-mesa-glx zlib1g bzip2 gpsd gpsd-clients xcalib libportaudio2". This worked. I tried to paste the next command....sudo dpkg -i <downloaded_file.deb> . But it came up with an error - syntax error, near unexpected token "new line".
Then I thought I would try to intall from the Ubuntu Software Centre and this worked....however I could only run opencpn from the terminal with the command "opencpn". I was able to install charts and recieve a GPS signal but when I wanted to close the package I couldn't...obviouly I needed to close the package in the terminal.
....What is the command???

It came up with the message gdk - CRITICAL**: 1A__gdk_window_get_Origin:assertion 'GDK_IS_WINDOW(window)' FAILED.
What should I do?
How can I run Opencpn from the desktop?
If I want to uninstall opencpn would I do this in the UBUNT Software Centre??? Or?

I'mn out of my depth. Had no trouble installing Opencpn with Ubuntu 10 version - this was easy

Any help would be appreciated

Marian