For a new user of Unix based OS's my best advice I can give you right now is stop using root. Even the most careful of people can make big mistakes by running under root. For operations such as installing software, changing permissions, and other super user tasks you can and should be using sudo:
sudo apt-get install node
sudo chown -R myuser.myuser /home/myuser
On the last Ubuntu system I installed node on the official repo gave me nodejs instead of node, so I used a different package. Which software package do you have installed? I know running under a normal user I had to make some changes to permissions when running under Ubuntu and using apt-get for global npm installs to work without sudo, whereas my Debian machine worked fine, but I also installed from source.
My course of action would be to start from scratch as a new user and reinstall node and npm. If you have some more patience and want to learn you should be able to work it out without purging node and npm, but you will most likely get running faster with a clean slate.